They are (were) certainly available from the factory... my 2005 passenger van arrived in the US with them installed
(option codes GEC and GEW on the original invoice: Front Left side sliding window and Front right side sliding window, $292 each)
On my datacard, they show up as "W18 LEFT FRONT SLIDING WIND. IN SIDE WALL/SLIDING DOOR" and "W19 RIGHT FR. SLIDING WIND. IN SIDE WALL/SLIDING DOOR"
In the parts catalog for that year, there's a page or two dedicated to all of the fiddly parts involved.
There's a slight
difference between the wall and door window sizes, hence different parts
The door window is about 39.5 inches wide (edge of frame to edge of frame), the wall window is 41.75 inches wide.
(also, they both slide forward, so there's a left/right difference due to that, too)
Here's the complete based-on-VIN parts page for my Sprinter's right-side (W19) window:
View attachment Sliding Door Sliding glass.pdf
(i note that the surrounding weatherstrip is the same for both W18 and W19 options)
I recall that there was a part number for the entire "kit" for either side's window assembly.
Added: according to the Dodge 2005 parts catalog file, the kit for a left sliding door's "vented" window is 5123 832AA
the kit for a right-side sliding door's vented window is 5123 834AA
(parts catalog files available at:
http://aie-services-2.net/Sprinter/ )
--dick
(if i can find the part number page, i'll add it to this posting) ...done