Source for Seat Belts
I bought a set of black belts with chrome buckles from ebay seller seatbelts-r-us. They are not exactly like originals but they are acceptable for me. The metal parts are actually made in Oklahoma! Great pricing at $58 per pair shipped (watch the ship charge on single orders as they combine). Sumitt also had some decent prices on Generic belts if I remember.
If you need reproductions or yours rebuilt you can try ssnake-oyl. Looks like good stuff but much more $$$.