I read an article in "Shotgun News" several years back about recovered WWII guns in Russia. First, you had the "hobbyists" who went to known battlefield areas and dug stuff up, mostly for thier own use/interest. Rifle wood was (but not always) semi-rotted, depending on if this stuff got into the perma-frost. Metal condition varied, but most were still shootable. There were pics of Russian cops showing off k-98's, moisons with original metal, but handmade stocks. Both metal and stocks had been cut down (for ease of handling apparently)by the criminal groups that these had been confiscated from. Most of the handguns/machine guns could be "brought back to life" with metal/machine work by any machinist I'm sure.
Second, criminals would seek these dumps out for obvious purposes. The thing that freaked the Russian cops out the most was reports of small underground ex-Soviet/wehrmacht dumps which contained artillery shells etc., some of whose explosive compounds were linked to organized crime bombings. Apparently if the Russian mob failed in obtaining modern explosives from corrupt sources, they fell back to these WWII sources!