Genius, people who buy cocaine and heroin by the ton have no trouble having their supplier throw a few cases of guns in the shipment.   You can buy a fully-automatic AK platform weapon in the ME, Africa, and much of South Asia and South America for a hundred bucks or less.  Brand name handguns are hard to get, but there are lots of serviceable copies out there.   There is relatively little flow of legally purchased weapons to criminals.   Most guns in the hands of criminals were illegally purchased by straw men, stolen, or smuggled.   Of course, not a few were put in the hands of criminals by the Obama Administration in their unbelievably stupid "Fast and Furious" gun-running operation.   No legitimate bad guy would be caught dead with a US legal semi-automatic weapon.   A US legal AK starts at about $800 and is semi-auto, the smuggled one is cheaper and is full-auto; crooks are generally stupid, but not that stupid.