They are called just that, weatherstrip retainers. The T-tops obviously only have a piece of that channel on the A-pillar. The front section on all the hardtop and T-top cars are black. The B-pillar color depends on the B-pillar trim piece color. If it's black, like say, on a Monte SS, the B-pillar retainer is black. If it's "bright molding" on the B-pillar then the channel will be bright.
If you DO happen to run across some NOS ones, here's the part numbers.
LH- p/n 20737665
RH- p/n 20737664
bright LH- p/n 20094267
bright RH-p/n 20094266
black LH- p/n 20094265
black RH-p/n 20094264
LH- p/n 20737667 (includes blowout clip)
RH- p/n 20737666 (includes blowout clip)
bright LH- p/n 20106333
bright RH-p/n 20106332
black LH- p/n 20106331
black RH-p/n 20106330
Blowout clips are p/n 20153291, need 2 if yours are missing and just need those. They come with the front retainers if you get retainers.