The seller that I purchased the sensor from is Buy Auto Parts . They sell quite a bit on Ebay. In fact, that's how I first came across them. If you know what the oem part number is on your sensor, or the corresponding Bosch number, they will cross reference it for you . Also, as I said before, if your someone who insists on only getting a genuine oem sensor, they're also an authorized Bosch dealer . And, they offer prices that are in keeping with many of the other online discount dealers . The link below is an example of their aftermarket sensor .
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=300472439656&viewitem=&sspagename=STRK%3AMEWAX%3AIT#ht_3173wt_1167