No one else mentioned them, so I will. Contact Cav Arms and have them build you one. Guaranteed to be 100% GTG.
http://www.cavalryarms.com/rifles.html
http://www.cavalryarms.com/rifles.html
I did'nt know much about AR's it was just what the fun store had, so I got it
not sure if that is a typo or on purpose but it fits either way.