THESE GUYS can set you up with a motorized bicycle chain sprocket that can bolt on to a disc brake hub mount. I am actually doing this for my next build, and no, to my knowledge no one makes a 68, or 140 spoke disc hub. In fact, I'm 99.999% sure.
Those high spoke wheels usually have a large flange that you can bolt a sprocket to.
Manic Mechanic used to make the sprockets.
The hub flanges had 2 small holes in them that you enlarged then added the other 2 holes.