Have you tried Palmetto State Armory? They are in your backyard. Might also try CMMG. Also there is
AR15 Sales. He sales Rock River and they make an A2 and National Match upper if that works. I bought a RR upper from AR15sales years ago and it was a no muss, no fuss transaction and the best price I could find. That was, however, pre-2008. -J