I believe Lyman used to carry it possibly still does, NEI I believe lists it, Mountain Mould would make you one. I have shot the 440 grain LEE real out of my 58 works well. Use soft lead to cast if you get a source of lead. the metplat of both the Maxi, REAL, are very small! ( the MetPlat is the little flat end on both, the tapper doesn't get wet when they hit, so it need soft lead to flatten and work.)

Veral Smith of LBT has a very good design of connicle for smoke poles, do a search and write him a note and I believe he can make you a real thumper for the .58. Veral has an in-house, in-stock mold sale on rigth now and has a .50 connicle double cavity mold on the list.

" 213: .512 400 gr and 310 gr in 2 cavity mold. 50 cal muzzleloader bullets for use without sabots or
patches. Band at nose fills grooves, rest of bullet is .499 to slide freely down bore. Base upsets to seal and drive bullet if pure lead is used. Blunt nose, very deadly game bullets. "