The closest thing I could find were ATV tires 14×9 but their load capacity fell short from what I am using the tires on (A home made rally/sand car.) The rim size will be 14×6 or 14×7 (depending on the selection of tires I find.)

I am planning on converting a 91 Dodge Colt in to a sort of semi sand car to off road in the desert around my area. The original wheels were 13s which I replaced with 15s. The next step was going to be getting larger off road tires for the new 15 x 8 rims. [...]