Purple, the barrel I recently installed on my M1 Carbine came from Tradex. It is made up of four different pieces, all sleeved over a liner. I was quite surprised when I received it and to tell the truth was a bit reluctant to use it because of its construction. I was wrong and should have done it a few years back when I purchased the barrel. It shoots fine. I don't know if it will maintain accuracy if it gets hot, like the old barrel used to but as it stands, it shoots quite well.
I was so impressed, that I am considering making up a liner for a prohib pistol so that I can get it reclassified as restricted.
I don't know if liners can be had in different diameter ODs. They only have to be 5-10mm longer than 470mm to be non restricted. There is no reason why they can't be turned down from a 30 cal barrel with a muzzle extension that is long enough and the same diameter as the original barrel.
The only reason I'm even mentioning this is if someone wants to keep the original barrel look, it might be the way to go. Other than that, have Bits of Pieces bring one in for you from the US or make one up, whichever is cheapest.