Call the folks at Deer Creek Products (
https://www.deercreekproducts.net/). Deer Creek bought up all the old CVA parts when they got out of traditional guns, and for years had the mountain rifles available as kits, either the Deer Creek Rifle or the Northwest Rifle. They also bought up the machinery and stock from Douglas barrels when that company stopped making them for black powder rifles, and Deer Creek made their own. The last I heard they still had barrels available, you need to ask what they have. Or, send the barrel to Bobby Hoyt (
http://tradmla.org/tmaf/index.php?topic=22533.0) and have him bore it out to .54. Just make sure he knows that it is a CVA barrel because the bolster set up is a might different from what you would expect.
The Alaska regs required a minimum of .45 caliber round ball for deer and black bear, .45 minimum with 250 grain bullet or .54 caliber minimum round ball for other big game when I lived there. However, what I read now is a .45 minimum for everything, no bullet specified. I may be missing something though. At any rate, with a .54 barrel you are good to go with round ball out to 100 yards. Even .50 R.B. is good; moose aren't that hard to kill.
From page 19 of the 2017-2018 Alaska hunting regulations:
You may NOT....
• Hunt big game with a muzzleloader, UNLESS: it is a shoulder-mounted long gun and is at least .45 caliber or larger with a barrel that is either rifled or smooth bore and discharges a single projectile.
• Hunt big game with a muzzleloader equipped with a scope, or using smokeless powder as a charge during any special season for muzzleloading firearms only.If in doubt, call Fish & Game!
-Kees-