Safir Arms Makes the .410 AR upper. Here is a link from Gunblast.com, this is an evaluation that was written up. Safir Arms T-14 .410 Shotgun Upper for the AR-15

That is the only one I know of. Just as a heads up though, most American Companies have their weapons parts manufactured in foreign countries. It takes a little bit more work to find a completely American Made firearm that is newly manufactured. Saiga's are top notch, no doubt about it.