You might want to check gunbroker.com the HS (High Standard) barrels are abundant and often can be found in near mint condition, if you have a later RR the F (Flannery) barrels were also used. They to are fairly common.Interested in this also. I wanted one to replace a pitted GI barrel in a Remington Rand. I found a correctly marked one some years ago on epay that was nice in the wrap, but the bidding was hard and costly. The only other thought would be the big gun shows, but I'm sure you tried this.
That barrel is sold.Found this on Gunsamerica
Also try 1911Forum & 1911.org
Not sure where your at in MD, but the gun show in Chantilly, VA usually has a a few USGI vendors.I've been wary of the barrels that turn up at gun shows in my area (md, pa) alot of the stuff I see I am very leary of. I am by no means an expert. There are lots of unscrupulous dealers these days. Not trying to be the next schmuck that gets picked off.