You can buy kits to build an AR15.I have gotten them from model1sales.com and akpartskits.com.
You get their kit and built it on whatever lower receiver you want.
On another note,you guys have AR's with 14.5 and 11.5 inch barrels?What about ATF regs that state that the barrel has to be at least 16 inches?
On another nother note,I was looking at some lower receivers on the websight of a distributor and they had them from various manufacturers,and I saw one that was 'California legal'.It had no mag well.It was a single shot.I was a little sad.