Does your car have B72 (colored exterior moldings) with B85 wide molding? I don't know jack about the nuances of Monte Carlos, but I know SS's had black trim. The SS's I've seen had a sort of wider but smooth black molding on the outside of the window sweep without a round bead. I'm guessing that's the molding you seek, right? The wide crap I'm used to is the Regal/Cutlass bright molding. That's a real POS setup there, but that's another story.
The GM part number for the outer sweep LH would be 20674284. RH would be 20674285. Some NOS ones on ebay right now. About 200 bucks with tax and they're at your door. Not cheap, but what NOS stuff is anymore? I believe these are not the entire assembly (molding and rubber strip), but I don't know how they actually come from GM.
1981-88 MONTE CARLO SS WINDOWFELTS SET PAIR NEW GM NOS 20674284 / 20674285 | eBay
Dixie Restoration Depot sells some aftermarket ones that fit the outer molding on SS. So they claim. Whole set for around 90 bucks.
78-88 SS Inner & Outer Dr Molding Sealing Strips (set of 4) (dixierestorationdepot.com)