Since the 7.62x54R is the ammo for the Soviet bloc medium machine gun, and for their sniper rifles, it is pretty much a certainty that it is still being loaded. The corrosive primers have an advantage- they last longer. Do not count on ANY surplus round in that caliber being non-corrosive.
There is steel cased ammo available that is supposed to have non-corrosive primers. Wolf, Tulammo, Brown Bear, all state non-corrosive primers. But a C3 said, you may not want to trust that fully. If I take a Mosin Nagant to the range I'm probably going to put at least some surplus ammo through it, so I always clean up with some hot soapy water through the bore. Then some WD40, followed by my regular solvent and gun oil.