Try these guys. They seem to
Try these guys. They seem to do a top opening rear window for an LT35 which should be the same as a sprinter. Give them a call.
http://www.vanbitz.co.uk/Volkswagen-LT-(95-06)—Offside-Rear-Top-Slider-(Green-Tint)—LWB-+-Fixing-Kit/1815.htm
KS