I would say that if somebody had all the access that was required, impeccable contacts, and infinite time and patience; they could probably produce a rough number for the amount of 7.62x39 produced by China and Russia with... mayhaps 60% accuracy at the most. That's just me guesstimating based on how I know lot numbers in factories work, and how records are kept. Provided the records were around, somebody could come up with a number that would probably be over half right - for those two countries.
But, consider: places like the Sudan and North Korea made/make it, as well as multiple combloc countries in the past. I would imagine that one would have reasonably good luck finding information for the Czechoslovakia/Czech Republic or East Germany, not so much with say...Albania. And that doesn't even touch on civilian loads of it from all over the place.
It's truly impossible to say. More than enough to kill us all dead, I'm sure.