I have a 1975 SX250 as well. Call Charleston Custom Cycles in Illinois at 217 345 2577. You can order everything from repair manuals to engine/transmission parts to wheels. He deals exclusively with Harley lightweights and they have cheap prices. Good Luck. you can email me at firstname.lastname@example.org if you have further questions.
Check out my SX250 at http://www.personal.psu.edu/dam5013/art003/assignment3.html