Yahoo Japan Auction thread...

[irritatedmax]

And for wheel searches specifically, you can drill down to more specific results to make a generic "10j" search much more useful. Just click the search filters on the left:

自動車、オートバイ (Cars, motorcycles)
タイヤ、ホイール (tires, wheels)
ホイール (wheels; there is also a "tire and wheel set" タイヤ・ホイールセット option, so you'll have to get tires removed but it will have different results)
18インチ (18 inch, or choose whatever inch size you're after on the left)

That really hones in a broad search to something much more useful to what you're searching for. And then choose "used" 中古 like mentioned above and you're really off to the races.