Welcome to the site, hope you find a desert tank soon. Maier used to make a handle bar crossbar mounted one quart fuel tank. Someone made a numberplate tank too. Madkaw is right, get a KX500 and the fourstroke guys will wish for tight trails so they can catch up.
Here in Michigan we have an extensive trail system. All trails are mapped, marked, legal and most get groomed. The Cycle Conservation Club of Michigan is responsible for lobbying, laying out and grooming our trails. Maybe your state has a similar group.
John