You know the bike will run fine without a thermostat, right? Getting a good seal is another matter. If you've still got your old malfunctioning one you can cut the core out of it and still use the OE style seal. A thermostat is almost purely an emissions device. A thermostat does not keep a motor cool, it's there to make the motor hot as fast as possible. A hot motor burns fuel more efficiently, cleaner. A cold engine burns a little richer, has the potential to carbon up spark plugs a bit quicker, but it will eventually reach operating temperature at idle, and a bit cooler on the road with a clean radiator and working fan. An active O2 sensor helps a lot on lean/clean fuel ratios.
All you need are the dimensions and temperature range for your thermostat to go down to an automotive parts store.