James,
I don't know of any sources other than watching eBay. You might also want to subscribe to the Yahoo FT500 Users Group & post an inquiry on their board. It automatically sends out an e-mail to approximately 1K FT500 Ascot owners. Here is a link to the group:
https://groups.yahoo.com/neo/groups/honda-ascot/infoPlease don't give up on the bike as they are truly a great bike to ride. Have you tried bump starting it in second gear? That is less than optimal, but you should be able to at least ride it that way. I sure wish Honda had included a kick starter as a back up starter. I guess they were confident enough in the electric starter.
Have you checked the "Classified" section on this forum? I think there was one or two bikes being parted out a while back. Meanwhile. I'll keep an eye on my eBay search & send you a PM if I find a starter or pinion gear.
Good luck
J.