I found a kreiger 20" 1:9 with a rifle length gas hole.
I got a vltor upper from CSTS added a NiB coated bolt from ATRS.
I was trying to source an adjustable gas block but I wound up going with a bolt on unit from the parts bin.
I sourced a RRA ff tube and dropped it all of at the smith as the barrel wasn't chambered.
Topped it off with a Nikon MR-223 4-12x44
I slapped in on one of my lowers, the one with the best trigger (a timney).
Over-all it's still a work in progress, I'd like to build up a dedicated lower, and build up some hand loads......
Norc crap yellow box groups 1.25" 10 shot groups at 100. Hornady steel match 55gr groups 5 shots into .85" @ 100. So I'm going to go out on a limb and say this tube is a good one (IMHO), now just to get a "more better" lower to complete the build.......
As a previous poster has already said, give ATRS a call, they may have what you're looking for....
Cheers!