Heavy Duty back Rim ?

First, a heads-up: what you're looking for has a price tag. But I've bought something like what you're asking about and it's very good. The price is right. Take a look at Pirate Cycles Worksman Wheels. He makes hub adaptors to fit those. The Worksman wheel will take some punishment. The hub adaptor will bolt to its hub, can be adjusted linearly, and the drive sprocket is bolted to the adaptor - so you can change to another bigger one or smaller one easily if you desire. I think Sportscar Pat makes an adaptor too, his should be pretty good also.

I've found my best results from using a disc brake wheel and replacing the disc brake rotor with the drive sprocket. Kings Sales and Service (see top left of the page for sponsor link) sells a top hat adapter that allows you to take advantage of the disc brakes and the bolt on to the rotor mount for your driven sprocket.

While I did not agree with the way I got this wheel. Was prelaced to a rim. I relaced it right away and it has been holding up to the Morini 9.4 hp motor really well. I like the concept of this. It is the same width as a basic 9 speed cassette disk brake hub would be mounting to a bike wise. I really like the disk brake on the right hand side. I want another one of these hubs but can't get it right now.

http://motorbicycling.com/f23/scsws-rear-disc-brake-rear-hub-10509.html

Other than this hub mounting the sprocket to the disk brake mount has been among my favorite set ups with the disk brake style hubs I have.