I don't know if this will be of help or not, but i believe i saw one of these for sale at a local bike shop.
You might call them to see if they have or know of any parts for sale.
Desert Sports Co. # 1-800-547-9888
Another place i know of that has worked on these old Harleys is:
Poor Richards Cycles: 1-505-324-9423
Hope this helps.
Good luck!