A good start would be to become a member here:
http://www.vjmc.com/
I've had good luck on some "restoration specific" parts here:
http://z1parts.net/products/vintage-motorcycle-parts
I'll have to dig deeper into some old links. I know I have at least 1 that is a Japanese site that may have just what you need.
Got any old pics o current ones of what you are working on?