>>even M1s from the USA aren’t going to reach Ukraine any time soon

No surprise there. As I understand it, warehoused tanks were all built with a Chobham variant that makes use of DU. It's top secret - and can't be exported. So new tanks have to be built. Getting something 'top secret' sent could be done with an act of congress, and could be faster - but have you seen the US government?

Of course, given the mess in Iraq from DU penetrators, I have to wonder how the US is going to deal with the DU armor once those tanks have been superseded.