AFAIK the only one you can't buy easily is 1.4 (which is the beta to 2.04, only distributed internally to CBM and also with A3000UX).
Even then, it's probably not worth that much, as there doesn't seem to be any software that only runs on 1.4, but never runs on 2.
Sorry. Not much of a market for ROM chips / Kickstart files.
It's for sure used rarely, but not rare in existence. It is in lots/all of the early A3000's, not just the UX. Most were shipped with the 2.04 ROM kickfile on the hard disk so they wouldn't ever know unless they knew the trick to get it to boot into the strange 1.4.
