[Foster]

I can't help you on the fabrication of the hubs.

On the other hand they look pretty close to standard bike hubs, so I would visit a few bike shops / repair places and see what they have for replacement hubs. I'd look to see what I could do some minor changes to and get them. The local bike repair guy is pretty clever, I'd explain what I was trying to do and see what he suggests.

It looks like you want to direct drive the hubs, can you get by with driving a small sprocket that's attached by chain to the drive hub of the wheel?

Good luck!