Atleast help on finding one or parts for one would be great as well.
all kx500 carbs from 89-2004 would work perfectly... stock carb is the keihin pwk 39... but you can also try to get a pwk 41 .that will add more top power for offroad or desert , but it needs a little bit bigger jets,because of the much higher airflow...
you could look on ebay or directly at the keihin websites (google search will help to find some )
some guys also use lectron-carbs or the smart-carb ... youll see, you have some options...