Where can i buy a variable speed, 12 volt speed control or rheostat for my cars a/c blower motor?

My Jeeps fan speed controler died. It's a work car and I just want to buy a variable speed dial and put the old knob back on it and re-wire it to the fan motor. The dual a/c replacement control unit is $680 from Jeep. Please help. Thanks|||Get one from salvage or off ebay. You can't use a rheostat to control a fan like that, the draw is way too high, and the speeds are all wired separately.