while not being able to offer any suggestion on who to send the wheel to for a repair, i have often drilled out the buggered up taper seat and reamed to a common "shank style" nut found on aftermarket mag wheels.
this almost always requires the shank style nuts to be drastically shortened [in a lathe] so they do not bottom out on the drum/disc before becoming fully tightened.
sometimes, however, the taper on that style of wheel can be touched up with a 60 degree "chamfer bit" as is commonly used in a machine shop.
can you post a picture of the wheel in question ?