I wondered about the same thing for several years. I've looked at all kinds of tires, and the only thing close to fitting was a temporary "donut" spare from a Jeep Cherokee. I think it was something like a T85-D15 - does that sound about right? The spare tire well is just at 6" deep and about 25"-26" diameter. I think the Jeep is supposed to have the same 5 on 4-1/2" bolt pattern I need.
Let us know if you find a good fit,
Jerry