Window track rollers?

Does anyone know where I can get the white nylon window track rollers for my Duster? I was working on my passenger door yesterday, closed it, and the track popped off...thankfully, the window was not in it or I'd be hunting for a new one.

I'm not really sure what they are called off-hand, but it's a white roller that pops onto a ball on the regulator and the roller rides in the track. From memory, the roller is about 3/4" by maybe 1/4"...I'll see if I can dig up the pieces and grab a pic.

Thanks.