I'd start my search with the most recent Walneck's Classic Cycle Trader magazine
It may not have the exact parts you are looking for in the parts for sale section, but most importantly, review all the ads for motorcycle shops with large inventories of older parts. You never know what you might find after a few telephone calls.
If they don't have what you want, maybe they can direct you to someone who does. Good Hunting. That's how I found nos parts for my 81 Yamaha XT250.