This is one of the fasteners that holds the fender chrome trim on. Where can I buy these?

 

This comes up from time to time so I recommend you search the forum for related conversations. For the record, they're for the quarter panel trim and not the front fender trim (no offense). You can get reproductions from Fusick but be forewarned: they are not all created equal. I've gotten some that work well and some that don't allow the trim to sit flush. Best I can tell it's luck of the draw.
Also, the originals have a small o-ring seal on the tooth. The repro's don't come with the o-ring so you'll have to come up with your own sealing method.