Parts? I'm guessing you're referring to the non-USDM version? IIRC, most just bought a new top however I think you could find a vehicle upholstery shop and have new plastics sewn in if the top itself is good. If you're talking about the USDM version, you can buy the one piece window and install yourself.
Hi Thanks. I have a non USDM, but its been covered in a one piece which is different to the US version. I don't know how easy it would be to convert it to us version.
If you're looking for just the plastic, so you can glue or tack it in, have a look at this: http://ahh.biz/vinyl/clear/crystal_clear_outdoor_vinyl_heavy_duty_40_gauge.html According to the site, a "yard" measures 54" wide X 36" long (approximately), so only 1 yard - at less than 30 bucks - would easily take care of a 4th Gen backlite! You'd have to get a good adhesive; I don't know that you're gonna get through that with staples!
