You essentially need to buy the entire quarter window, unless you are just talking about the plastic covers. Quarter windows are relatively easy to refinish with a little bit of time and effort. A couple cans of flexible filler-primer, some wet-sanding paper, and some semi-gloss flexible trim/bumper paint is all that's needed. I refurbished mine in a couple of hours after pulling them out of the car.
Yeah, that trim is NOT removable. There is a company that makes covers for them, but for the cost, you are further ahead to refresh them on your own. Clean factory look > goofy covers. Do a search for window trim in both tech and talk; there have been a few very detailed threads on how to go about refinishing them.
Not meaning to hijack the thread or anything but has anyone ever painted that along with the black edges or the door a different color? I'm curious to what that would look like.
It looks nasty, very very nasty.