gear drives
I am sure that gear drives for your SBM is made, and like you I dont see them in the usual sources. I would recommend getting a copy of MOPAR Magazine, or possibly one of the Off- Road or 4 X 4 magazines and look in there for a company that Specializes in MOPAR performance parts.
From personal experience, I would stay away from JC Whitney. Ive had bad parts come from them, lousy customer service, their prices arent any good deal, and they charge the highest prices for freight and ship the cheapest way they can.