Mike: You won't need to get BATF involved since they don't consider a muzzle loader to be a gun. It should not cost more than $200.00 for someone to collect the gun, box it & ship it to you. As Ken said, getting someone to bring it as checked baggage could be a pboblem. A couple years ago I went to England and bought several guns from Holt's and Bonham's. I took along two big suitcases thinking that I could bring them all back. WRONG! I did bring back a muzzleloader 12 bore marked "RADCLIFFE & GUIGNARD, COLMBIA, SC" which is my hometown (bought it from Holt's) I had no trouble getting it on the airplane at Gatewick. When I landed in NY at JFK I thought they were going to send me to Riker's Island. I had to wait at U.S. Customs for over an hour until they could get a cop out of N.Y. to come and tell them that it was an antique and could not be fired with modern ammo. I just sent two antique SxSs to England by U.S. Mail and the cost was $89.25. Smallbore would be a good choice or John Farugia at Cheshire Gun Room, Stockport Telephone 011 44 161 480 8222.
Best Regards, George