Check with Muzzleloader Buidlers Supply[url]
http://www.muzzleloaderbuilderssupply.com/[/url]
or Pecatonica[url]
http://www.longrifles-pr.com/[/url]
I don't know of anyone who makes the same stock as the blue ridge, which is a good thing, but they may have something you can use.
I would suggest replacing the lock with a good one, preferably one of Chambers locks, and replace the hokey screw on barrel mount with pins. It would also be a good idea to replace the hokey thimbles with correct ones.
IMHO, the only really good part of the blue ridge is the barrel. IMHO, the locks are junk, but the barrels are usually pretty good.
I would suggest a southern style stock, if you want to reuse the old buttpiece, trigger guard, and triggers.
However, IMHO, you probably would be better off building a better gun from the ground up. You probably will invest a good bit in just replacing the stock, lock and thimbles, so why not spring for a little more and build a decent gun.
That said, could you post a photo of the crack?
Someone may know how to repair it.
Just offering a few options.
J.D.