Not a Chevelle, but my Olds, however, part should be the same.
I'm replacing all the almost-40-year-old rubber, and the one part I haven't had any luck finding replacements for yet is the seal for the vertical part of the quarter windows. The upper channel is the same as the channel for the door windows, but the quarter appears to have a slider track with fuzzy seals on the sides.I'd presume this bit is similar on all post coupes, but I've found nothing for *any* year post coupe. Thank goodness the vent window rubber and window channel are the same as those on an El Camino...
Anyone have any experience with this?

post cars were not produced in Chevelles after 1969.
You might want to ask one of the guys on this site with a post sedan who can help you.

Did not know that, but I can't even find mention of this part for '68-9 post coupes. 4-door stuff won't help because the rear door windows work the same as the front, and my, doors. Post coupe rear quarter windows are unique, apparently.
I need to get pictures - it's hard do describe what I'm looking for.
Thanks for the info, though!

I just bought a full weatherstrip kit for my 69 chevelle malibu. It came with everything but the trunk seal. I had to get that some where else. It did come with the two quarter strips you are talking about. I got the kit from a company on ebay. I noticed there were a lot of weatherseal kits for different cars on there. You might try and check there if you haven't already. Let me know if I can help you with anything else.

Is your '69 a post coupe or a hardtop? Mine's a post. the two little strips that go on the leading edge of a hardtop quarter window do me no good, I'm afraid. Pity, because those are *everywhere*.
I think I need to post a picture of what I'm looking for.