Ok, first things first.
...and you should have maybe started with telling us that this GTO is for sale on that site
and provide us with the actual link for it.
http://www.gepimped.nl/car/volkswagen-polo-86c-g40-rieger-gtoAs it turns out, this gives us the cell number ( phone number ) plus location of the current owner
AND it gives the option of sending this guy a message...
As for getting one of these kits... I know its sounds very unlikely, but... how about trying
http://www.rieger-tuning.de/The catalog is online, goto page 340...not exactly
rocket science.
Since this is not exactly just a bolt on kit, making it fit on a steilheck shouldn't be much of a challence.
But then again...so isn't finding the info above
You've been helped !
Good luck !
Mark
Canada