Glock doesn't make a carbine... YET. Hopefully! The rumor has it that Glock is supposed to have one by 2006 or somewhere near. The carbine you are looking at is a Mech Tec. You can buy them here....
Mech Tech Carbine Kit
http://www.popguns.com/mech_tech.htm
There also another carbine kit for the Glock which you can get here.....
Impulse Carbine Kit
http://glockmeister.com/catalog/prod...roducts_id/315
I have read reviews on both but have yet to fire either. The reviews sounded pretty good on both, not stellar accuracy but good enough for human sized targets.