I have bought some Wilson Combat stuff so now I get marketing emails from them, thanks guys... I just noticed one of their emails is about Glock barrels. They are making barrels for the 17, 22 and 21. Will not fit the Gen 4 series!!
http://shopwilsoncombat.com/Glock-Accessories/products/169/
http://shopwilsoncombat.com/Glock-Accessories/products/169/