I was lucky enough to find mine right here on this site. My suggestion, if you're not in a hurry, is to search every classifieds section you can find relating to racecars. Don't just look for panasports, look for whole race cars being sold. Often these include extra sets of wheels, and the seller may be willing to separate parts from the group for the right price. I frequently (relatively) see ITC civics and ITA CRXs/RX7s being sold with 8 or 12 *extra* wheels. When you find them, be quick about it. There aren't many 14x7s available, as I'm sure you know.

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'88 CRX Si - ITA/PS2 road racer: Handles like it's on jack stands
'98 ITR #0231 - DS autocrosser: Handles like I sold it
'02 Jeep Grand Cherokee - daily driver/tow vehicle: Handles like a jumping castle