Thanks for the suggestion on Aim surplus. Their uppers with Daniel Defense barrels or Spikes components look like exactly what I am looking for. I read a number of reviews and it appears they are excellent and reasonably priced.
Their stripped lowers look well priced as well, though I am going to try to find a private seller in the Denver area if I can. I have bought three guns in the last year and a fair amount of ammo online, so I think I want to stay off the RADAR for the lower if I can. Living in Denver after the Theater shooting, I think the local officials are keeping a very close eye on things.