http://www.cheaperthandirt.com/product/77473
Take a look at this one if money is a concern. I do not believe that building one is a practical solution economically unless you wish something out of the norm and are willing to pay quite a bit extra for it. The one above is a good price, for myself I paid the price to have a all stainless. If you don't intend to get other barrels for it I recommend you look at the two main versions of the Triumph it is a dedicated muzzle loader and dose not have the problems and tolerances needed for a switch barrel gun.