I don't know of anybody who makes aftermarket barrels, the factory sells barrels for 1/3 the cost of T/C barrels and that's pretty steep competition. Some, like David White, will cut off a shotgun barrel, thread the stub, and install a custom barrel, but the cost is pretty high.
Three ideas:
1. Find somebody who's getting ready to order an extra barrel for his rimfire and get him to order a .17HRM for you while his gun's at the factory.
2. Buy a $90 .22, send it in for a .17 barrel, sell the .22 if you don't want it.
3. Buy a $125-150 .17 HRM, sell the stocks for $50 on eBay, sell the receiver for whatever you can get for it, and ream the barrel to 17AH.
If possible, make sure the barrel from the centerfire rifle will close & latch on the rimfire frame. It's still possible the rimfire barrel won't close on the centerfire frame, but it's easy to remove material from the barrel, much harder to add it. If you have lots of rimfires to choose from, pick one that will swap barrels in both directions with your centerfire.
It sure would be fun to have a 17AH/22AH combo on the same frame, wouldn't it?