Dorman sells some universal clips, but you need to have them in your hand to make sure they will fit and hold the way you want them to. Some hardware stores used to carry them. I wouldn't order any from a catalog unless you know for sure that they will fit your applications.
A few of the repro parts suppliers carry some body side trim clips but not for all applications. You may get lucky by investigating.
If worst comes to worst, I have manufactured my own clips from strips of spring-steel that I would cut out with metal sheers, then drill a hole for a pan-head machine screw. Put the screw into the hole and weld the screw onto the metal, then grind the weld down so it allows the clip to fit into your moulding. This method is only good for clips which can be accessed on the back side to install rubber washer, flatwasher and machine nut. If possible, try to use OEM clips in areas that have poor access behind, or for these locations, you might be able to modify a Dorman pop-in clip.