250 TT250

I am looking for a choke plunger for the Mikuni Carb on a 1980 Yamaha TT250. I just can’t seem to find one anywhere. The plunger on my carb has a worn rubber piece at the bottom that does not seal...would anyone know of a place to get rare parts like this?
Thank you
The part shows up on microfiche but no one offers it...as far as I can see. No worries, I think my little piece of tubing will work...until it doesn’t....lol