When I wanted a flinter I asked track and it was well over $200 total. They remove the breech and fit it with a flint one. That voids the warrany though. If I were you I would get the TC 58cal flint barrel. The 1-48" twist will shoot roundballs just fine and some nasty conicals if you ever wanted to try some. Plus, you do not have to modify it and void the warranty.

Here is another choice, this will cost a little over $200 to but you can customize it. Tell them 58cal flinter and choose your length and twist. They come in the white so you can brown it yourself. http://www.thegunworks.com/custprodgun.cfm?ProductID=528&do=detail&Ca t2Option=yes