I am from Canada, so not sure if this site can help you with parts or not. But I have found an awsome place in Edmonton Alberta, who also sells via internet, that has tons of old bike parts along with old bikes in general, and they are great help. Go to.
http://www.recyclemotorcycles.com/
It wouldn't hurt to see.. good luck.
I am currently rebuilding an old 1975 RM 250 and this place has helped me alot.