Make no mistake about it, the West isn't actually running out of anything critical, it simply comes down to the political will to support things. Here are some examples.
Main Battle Tanks
The United States
has more than 5500 M1A1 and M1A2 Abrams MBTs. More than 3000 of those tanks are being stored, with no intention of using them again, as the U.S. continues production of newer versions to replace them. The United States has committed 31 of those Abrams to Ukraine (they'll arrive in the fall) and could easily send them 500 of them (pulled from storage) without degrading their Army's fighting capacity at all. The Marine Corps literally just retired more than 400 M1A1 Abrams as they move to lighter vehicles, and had no plans for those tanks moving. They could be sent to Ukraine by year's end, without the U.S. military blinking
Germany
and Belgium
have a combined more than 350 Leopard 1 MBTs in storage. Some of those Leopard 1s belong to arms dealers, who supply want to sell them to the Western governments at hyper inflated prices. Again, that's a political decision to negotiate for them, but those Leopard 1s are absolutely available. 130 of them have been promised so far. 220-300 have not been, but could be.
Germany
and their private industry also have approximately 50 more Leopard 2 MBTs in storage, requiring modernization before being sent to Ukraine. This can be done at any time. Rheinmetall can get several out the door each month, they just need somebody to pay for the contract. Meanwhile, they're buying 25 more back from the Government of Switzerland
than which can also be sent. I estimate that Getmany (through private industry) could send upwards of 75 more Leo 2's to Ukraine, without taking anything from their own army.
Poland
has purchased 1000 new K2 MBTs from South Korea
and 250 Abrams from USA
Their plan is plan is only to feature 2 MBTs in their army, which means the remainder of their PT-91 Twardys and many (eventually all) of their Leopard 2s can be sent to Ukraine as their new MBTs arrive. They possess approximately 100 PT-91s and T-72s that are completely expendable at this point and could be send to Ukraine ASAP. As for Leopard 2s, they probably won't send anymore right now, but as their Abrams' arrive, they could probably send 40-50 more prior to the end of 2023 and into early 2024.
Britain
has approximately 230 Challenger 2 MBTs, of which, less than 150 are planned to be upgraded to Challenger 3 and remain in service into the future. Britain has donated 14 Challenger 2s to Ukraine. They could triple that number to 42, without changing any of the long term plans for their tank fleet.
Czech Republic
has been modernizing T-72s bought up from around the world by third parties and sending them to Ukraine. Thus far they've modernized about 60 of the initial 90 that were purchased from third partied by USA
and the Netherlands
. Another 40+ are already marked for the next contract, as the world is scoured for more sellers. By time that Czech initiative is complete, they'll likely to have send more than 150 modernized T-72s to Ukraine, paid for by third parties. They have about 90 more to go.
Between Canada
, Spain
, Sweden
, Finland
, Norway
, Greece
and Portugal
there are roughly 40-50 more Leopard 2s that could be donated as soon as a couple months from now. Again, there would have to be the political will to make it happen.
Both Cyprus
and Morocco
have significant numbers of T-80 and T-72 MBTs that they are looking upgrade with Western tanks. Morroco is purchasing an undisclosed number of Israeli Merkava 2/3 MBTs and the rumor is that the West is going to buy all 158 of them (T-72B3), further upgrade them and send them to Ukraine. Meanwhile, Cyprus has 82 T-80s that Ukraine also wants. Cyprus is rumored to be the second European buyer of the Merkava 2/3s. We could very well see a Western deal where NATO countries purchase the Israeli tanks for Cyprus, in exchange for their T-80s, which would then go to Ukraine.
Pakistan
is another interesting source for tanks. The Pakistanani economy is in shambles and they've already been selling arms to Ukraine through British funding and German ports. Pakistan has 320 T-80UD MBTs that were sold to them by Ukraine. The Pakistani government has made it clear that at the right price, they'd be willing to sell some of them back. How many exactly it's hard to say, but it certainly wouldn't be an insignificant amount.
Finally, Ukraine
has anywhere from 300-500 T-64, T-72 and T-80 MBTs in longer term storage. It was announced just recently that Ukraine is partnering with Rheinmetall to modify, modernize and repair these stored tanks. Ukraine will send their own engineers and experienced employees to Germany and they'll run the project, with the help of Rheinmetall employees, at their German facilities.
Right there I just showed you 1000-1500 more MBTs that the West could purchase for / send Ukraine, without taking away from their own combat units at all. That represents more tanks more tanks that Ukraine has had since the beginning of the conflict.
How about infantry fighting vehicles?
The United States
is building 700 new Bradley M4s and will be replacing nearly 1000 Bradley M2 ODS (the model being sent to Ukraine). The USA can easily afford to send 500-700 of the older Bradley variant to Ukraine. They have more than 4500 of them in operation and they've only committed about 150 of them to Ukraine so far.
Britain
has more than 700 Warrior IFVs that they are in the process of being replaced, with deliveries having already started this year. While it will be some time before all of their older Warriors are expendable, they're certainly able to ship a percentage by year's end. The first 100 Warrior IFVS could be in Ukraine by the fall if the political will to get them there exists.
Similarly to Britain, Germany
has approximately 400 Marder IFVs that they are in the process of replacing with Boxer AFVs. Germany industry has between 100-200 more in storage. The Germans have committed to sending 60 Marders to Ukraine so far. They could easily double that number by the end of 2023, simply by paying to have private industry sell them out of storage.
Between Sweden
, Norway
, The Netherlands
and Finland
. they have more than 1000 CV90 IFVs. Thus far Sweden has stepped up to send 50 of them to Ukraine. Those 4 countries could easily combine to double that number to 100, sending an additional 50..
France
has 250 AMX10-RC AFVs that theybare currently replacing. They've committed 40 to Ukraine so far. They could easily double that number to 80, by sending 40 more, as the vehicle is being phased out of their military.
Poland
is sending Ukraine 150+ Rosomak IFVs in a deal that was announced last month. Some number of those units can and will be sent to Ukraine right away, with Poland backfilling their own military using newly purchased ones as they roll off the assembly line. Roughly 100 will enter Ukraine during 2023, with the rest to come throughout 2024.
There is roughly 1000 more IFVs that could be donated in very short order, without damaging the integrity of the militaries of any of those nations.
Therefore, I just listed upwards of 2500 MBTs and and IFVs that the West could easily send. None of it's new and none of it is imporant to the fabric of any Western military. I could go on and do the same with armored personnel carriers, MRAPs and artillery, but I think you get the point. It's not correct that the West is running out of armor to send Ukraine. They have more that they could afford to send in the future, than they've already donated to this point. It's all about political will power, Ukraine's continuing will to fight, and how badly NATO wants to neuter the Russian Army.