I've got a few bits left over from a 75 250 enduro I didn't go ahead with, including a few axles & front and rear backing plates. Just send me the OD & length of the axle you need, and I'll have a look. I don't think there was much change in the backing plates from 73 through to 77, and I've got at least one I don't need at present.
Cheers, Mike