There might be several companies that restore seat belt mechanisms, but its a bit tasking. Friend had to fix his since the driver's seat belt was ripping up (security concern), and went with
www.safetyrestore.com. They give you a seat belt webbing color chart/samples for you to pick your desired color (similar to shopping for house paints). Then you have to remove the complete seat belt assembly and ship it to them.
However, they screwed up my friend's order TWICE (supposedly because they were moving to a newer, bigger facility). Still, their work is top notch.