Thank you Dave
As I hope you know it, please note that this engine is made by Microcosm then sold by two or three resellers on eBay for example.
I don't know if they have stock of spare parts to send in case of customer request so I think you have been advised to buy one and I expect this will solve your problem, despite the fact other members of this forum didn't give yet an opinion.
If you wish following my (misa)dventures with my Hit & Miss engines, don't hesitate to have a glance to my "Hit and Miss et autres moteurs" YouTube Playlist
https://www.youtube.com/@rhavrane/playlists and you will also learn French