I need new and haven't found any NOS pairs...

Carparts

ive bought from them.. whole front-end basically for my '98 blazer
theyre kinda steep on their shipping, but they offer an awesome shipping discount if you buy more than one item

if it's just belts you need, could probably find a better price shipped elsewhere, but they were great to deal with and didnt have any problems (and that included a new hood undamaged)

I've used these guys:

http://wescoperformance.stores.yahoo.net/seatbelts.html

These guys will rebuild your OE: PEParts..