The hardest to find are the Vietnam era Chromium-lined M3A1 barrels.
Now you have got me trying to remember!
When I was stationed at Fort Carson (1979-1980) we had M3 Grease Guns issued.
In Germany (1980-1984) we had the M3A1 issued.
I shot them and cleaned them.
Downrange at Fort Carson I even fired one at infantry targets from the loaders hatch! (Fun time that was!)
I went to the unit Armorer's course and spent time in the unit arms room both in the USA and in Germany.
I spotted chrome lined 1911A1 barrels, but don't ever remember seeing a lined Grease Gun barrel.
We didn't shoot any of the .45 caliber gun's much in Germany due to a shortage of .45 ammo for training.
I do remember a friend burning his hand on a Grease Gun barrel after walking off the range, I still remember that sound followed by his yell in pain.