Probably the easiest and most cost efficient would be to get a .450 Bushmaster barrel, same rim diameter and plenty of factory ammo on the market. Several companies offer "Remage" (barrel nut type) barrels to make it a DIY build.

Charter Member
Ancient order of the 1895 Winchester

"It's an insecure and petite man who demands all others like what he likes and dislike what he dislikes."
szihn