my bet is the soviet AK are the most plentiful throughout the world............you have to remember the soviets gave, or "loaned" them out to any country to favor that county to side with them, by the train car loads, especially in africa, sub-sahara region, not to mention centeral American countries, and VN......which sided with the soviets after the fall of saigon.
next to the US, my bet is that the soviets gave out on credit, or payment more military hardware, ie. small arms, ammo, tanks, aircraft, missiles then the US ever did..........if you look at any thrid world county's inventory of military equipment.........you'll see there are more MIGs in those country''s air forces, and T-series tanks, then there are countries with US made equipment......AKs were probably just a freebie for buying the big dollar stuff