Umm, in pretty much every country except Russia it is completely legal to violate Russian state secrets, and in pretty much any country other than USA it's legal to violate USA state secrets. The international buyer should be completely in the clear.

Furthermore, it's very likely that the seller also is completly legal - as long as it's outside of Russia but one of ex-USSR republics, their new legal systems generally don't prohibit distributing USSR state secrets, only documents that are classified by their own new authorities.