I think there's a slight misunderstanding. Paughco makes some nice HD replacement drums (although their catalog now says drum sales are limited to stock on hand - looks like they're gonna stop making them.)
No one makes a conversion drum setup to convert a disc brake wheel to drum brakes. Why would they? If you're gonna tool up to manufacture something, you want to build something that would sell, at least enough units to recover your costs of tooling and make a little profit. I don't think there are many instances of guys wanting to put drums on disc brake wheels. Most guys change brakes because they want better brakes.
Doesn't mean it couldn't be done, but you'd probably have to re-engineer the wheel itself, or maybe use a really narrow drum, like a Sportster drum and re-engineer that. Easiest, I think, just to set up the frame for a disc, or put that wheel back on the shelf and set up a drum brake wheel.