The main muzzleoading barrel companies, Colerain Barrel Company, & Rice Muzzleloading Barrel Company, will be more than willing to fabricate a tapered round barrel for anyone that requests one. So will the one man barrel makers like Bobby Hoyt, Ed Rayle, Howard Kelly, and Charlie Burton.
Just remember that the little guys have backlogs. Rayle is at 3 years, Burton is at 1 year, Hoyt is at 1.5 years, and I don't know what Howard Kelly's backlog at Webertown Rifle Works is.
Special Orders at Colerain, and Rice, are generally performed only 1-2 times per year.