Steve Tasitritsis 'ATLAS ARMS', 2704 N Central, Chicago and (later) 7952 Waukegan Rd. Niles, Illinois offered replacement barrels for Smith and Parker guns in the 50s and 60s using tubes made by E.S.C. Vickers (England) and fit and finished by Armaf in Belgium
http://www.littlegun.be/arme%20belge/artisans%20identifies%20a/a%20armaf%20fr.htm

Parker barrels with a 1954 lettre annale



Semi-finished barrels as Bro. Larry mentioned, in all gauges



Looks like Atlas had an in-house gunsmithing dept.