I reused my original rubbers and they were out of the car for 25 years. I just cleaned them real good with thinner and a scotchbrite pad. The repro ones look good if you can get them to go in correctly but they don't last, they just don't have the quality rubber that was used 45 years ago.
New ones can purchased at your chevy dealer there rounded not squared like original, but width is identical(chevy s-10)
mine was chrome they may have it in black
That is what I used for the insert also, I bought a 100ft role through my buddies glass shop. (Enough to do 3 cars) The GM stuff is almost an 1/8" narrower than the original. The only issue is the corners on the front of the rear glass don't lay exactly like they should but unless you are as picky as me you won't notice it.