Realistically, here in Canada, you usually pretty much gotta order and wait.
One of the guys I would suggest checking with fairly soon in the scheme is to talk to the Rusty Woods Trading Company, as they deal a lot more in the cowboy action shooting world than most, and if anyone has a rifle size barrel blank in a pistol caliber, like as not, them. Possibly a take off that can be set back, if the markings, etc. do not bother you too much.
Another outfit worth checking with is Bits of Pieces, also in the BC Lower Mainland area. They deal in Green Mountain barrels, and 'might' hold some stock if you are lucky... Worth checking out GM's site and seeing if they actually offer the caliber. I know that they offer Winchester 1885 profile barrels, ready to thread and chamber.
Otherwise, it is pretty much an order and wait scenario. Filling out the forms for own use, and waiting for it to all fall into place, is the cheap way, paying someone else to do the same thing, or paying for the amount of profit they need to make to allow for the money tied up, is the other.
I think the only thing you are really off base upon, is the assumption that every gunsmith keeps a bunch of barrels around, which, I am sure they would like to, but I suspect that the cost of holding a bunch of stock loses out to the need to pay the bills, and eat.
IIRC, it was one of the pro 'smiths that said he recalled barrels at $12 each, at a time when a working man made a couple times that a day, vs. the money that can be spent now, amounting to several days wages.
Cheers
Trev