A German Motoparts website that offers seat cowls for the GS:
Wild Hair Accessories has tail and seat combos for the GS made by Gimbel (about halfway down the page):
Airtech makes a tail section for the GS that replaces the side plastics and covers the passenger seat (about halfway down the page:
You never know what a search on eBay will turn up or a browse through the For Sale section here on the forum.
this mod requires the gs subframe to be altered to fit the plastics and seat(modded by iceman oz)
another r1 plastics
The thread can be found here but the picture links are broken: http://gstwins.com/gsboard/index.php?topic=27240.0
Bear in mind the SRAD seat unit is from a very large bike and looks very large on the gs. :d
For this mod the complete GSXR SRAD subframe was used (although it can be acheived by modifying the gs's subframe) This step by step was done using the SRAD aluminum subframe.
from the center of the tank mounting bolts and at the bottom 230mm from the engine side of the frame (it was the only place I could get a consistant measurement from)
There are many examples of custom rear ends done to the GS on google. The possibilities are nearly endless with time and experimenting!