You can find the Advantage Arms 22LR Conversion Kit for Glock 17/22 Gen1-3 MOD here.

The Advantage Arms 22LR Conversion Kit converts your 9mm/.40 S&W Glock to 22lr. Includes two 15 round magazines, a 4.49" Threaded Barrel, a range bag, and a recessed cut optics-ready slide for a variety of red dot options. Slide includes iron sights. Red Dot and Handgun Not Included. 

Firearm: Glock 17/22 Gen1-Gen3