I would try to find some Russian forum - it is possible that somewhere on Russian market it is possible to buy what you want.
@APUGers from Russia: in Russia ebay is best know auction site, or you have some local one?

Since I lived in Poland - I know that on www.allegro.pl you can find full length films on 35mm format, but last time when I searched I did not found classic ones like Tarkovsky, Eisenstein ...