Please excuse any incorrect terminology. I'm not a mechanic and I'm a newbie rider, but I'll do the best I can to explain what I mean.
A few days ago I took the carb apart (for cleaning) on my '81 Kawasaki CSR 250. In the process I broke the butterfly valve for the choke.

I've been searching the web and the cheapest carb that I can find for a CSR 250 is $316. Kawasaki discontinued this carb a while ago so I'll have to get a used one. I'd like to only replace the butterfly valve but I am having no luck finding one.
So, my questions are... Where can I find a carb for an 1981 Kawasaki CSR 250 (for cheap)? Is there more than one carb that will fit this bike? If so which ones? Is it possible to purchase only the butterfly valve instead of the whole carb assembly?
And to add another twist to the story, I'm taking the MSF course this coming Monday (7/16/07) so I will need a fix by Monday morning. Am I out of luck? Sorry for the long post, I’m very frustrated at the moment.