Which kind? I have a set from a '75 in decent condition but they are the non-rectractable kind.
http://community.ratsun.net/topic/51833-620-parts-for-sale-san-diego-ca-updated/
Is it a king-cab or single? I think the length of the part attached to the buckle is different.
Most belts, retractable or not, will have some sun damage or fraying, so you might want to consider going aftermarket. Here's one option:
https://www.seatbeltplanet.com/