You need to strip more, gather all the singles you can and put a large down payment. Yamaha was once the easiest bike credit grantor but with the economy bad they've tightened up some. I think $3000 down might get you done. Talk to your audience and prompt them to cough up the 5s and 10s. Ones...
I think you're right about the transmission. You might want to think about the never ending cycle of repairs and money spent. All those new parts and now a tranny maybe. You're close to exceeding the car's value unless it looks really good. Time for a new one.
No problem. Any motorcycle salvage business should have what you need. The belts last nearly forever and the 454 and 500 Kawasakis were big sellers. Then of course there's always the Kawasaki dealer who can get you one, or may have it in stock.