No supply, increased demand and more black market.

There are guys in the Hindu-Kush that are making AK-47's for the Taliban on equipment that was portaged up there by Gunga-din and his relatives during the British occupation. 

It doesn't take a high tech shop to make a firearm or an assault weapon. The average brake and muffler shop has probably 90% of the gear needed, and the capability to make the rest.

If some tweaker can make meth in a bathtub, a teenager with a couple of high school shop credits is more than capable of building an AK.