I might be thinking of the wrong thing, but I've never seen plastic rocker moldings. The only ones I know of on the Regal were stainless and they are 3 pieces per side; a short section on the 1/4's behind the doors, the lower door sections, and the actual rocker sections that wrap up into the lower front fenders. The clips that hold the door sections are plastic. But there are metal stud clips on either end with nuts. I think the base models may have had a thin strip available, but I haven't seen that version in a long time.
There is a salvage yard that had 50+ G-bodies not long ago, and 2-3 Regals that I tried to get the moldings off of because they looked better than mine. It seems like many were sold/crushed, and also the last time I was there my Regal was broken into and vandalized for no apparent reason. Southern Delaware, so it would be a 8hr. ride from Erie (I'm originally from that area). There's another one sitting in the impound lot at a performance engine builder/service shop that looks abandoned too.
There was a Regal just like mine in a salvage yard outside of Brookville years ago. I was looking for a front corner lamp at the time when we went back for Thanksgiving (it didn't have it. I don't remember the name of the yard, possibly Christini's, but the car is probably gone by now (that was around 2006-2007). You might have better luck at a yard called Chapman's near Dubois, which we visited a day earlier. Looks like they have a website now,
http://www.chapmanautoparts.com/ . That place was huge, and was actually mainly older cars. Several G-bodies, including a blue '85 or '86 442 t-top car, which didn't seem to be in too bad of shape at all, but had no wheels, engine, and of course the t-tops were gone/off, and the interior too, didn't look bad, but the seats were soaked. Very odd as the paint looked original/shiny and no/very little rust (western PA!?). All the Regals either didn't have header panels or were '81-'83 models with different headlight bezels/corner lamps, so they didn't do me any good.