While I respect your desires to have easy to acquire magazines, there are alternatives. Midway USA shows 3 different mags for the AR in 7.62x39mm.
True, they aren't easy to get. But I'm sure there are other sources.
Part of the beauty of the AR style rifle is the simple detachable magazine. I am looking to build one of these myself. But keep the AR style magazine.
I wish you good luck in setting yours up the way you want it.
NRA Chief Range Safety Officer, Home Firearm Safety and Basic Pistol Instructor
"The democracy will cease to exist when you take away from those who are willing to work and give to those who would not."