Oh man...didn't realize that. I got mine locally at chevyland.com (a little pricey but was in a pinch). I checked out the truck and car shop and found these:
http://www.truckandcarshop.com/trucks60_72/t60_021.html
The only problem is that they don't look original at all and are just the folding type of latch buckle. If you're ok with that, then you're good to go. The rears are just non retracting belts. I think I have a set of parchment (or tan) ones in the shed from mine, but they were pretty dirty and I wanted black more than original...if you want I can take a look for them.