There's some old Unichrome paper for sale on ebay. I wonder if it's still any good and how on could try processing it. Reversal RA-4, as discussed elsewhere? Or would somebody (PE?) know how to mix R1000 chemicals?
I've checked recently some sealed R-3 paper from ebay (exp. about 1997-2005) - unfortunately, It's all dead. It has heavy pink fog and one box - a lot of fungus. Angifog agents do not help. Perhaps, if you will find deeply frozen paper, then you will get a chance, but I think it will be unlikely.