I'm not sure which moldings you're referring to. There could be molding down on the rocker panels, at the top of the door where it meets the window, and at the middle of the door at the peak. Classic Industries has a pretty complete section on exterior molding and clips. www.classicindustries.com
. I've found you need to check all the Camaro suppliers because no one stocks everything.
Body shops buy this kind of hardware from Paint & body equipment jobbers; stores that sell nothing but automotive paint and supplies to support the body shop trade. You can take your molding to them and they can match it to a clip that'll work for you. If they don't have the clips in stock, ask who they buy from and go see them. We have one of these huge suppliers in Columbus, Ohio named Kimball Midwest. They carry automotive hardware from a company named Auveco. They clips shouldn't be that hard to find, but considering the car is 40 years old, I could be wrong.