Actually, the Glock 23 is a .40S&W handgun. The .40S&W is already at +P levels. There have been a couple of companies in the past (Corbon & Georgia Arms) that sold a .40S&W +P round but I have never seen a +P+. I actually have one box of Corbon 165 gain +P left.

Now as to the 9mm (#17, 19, 26 & 34), Glock will tell you yes to shooting +P in them. However they will proably reserve the +P+ for the military and police. (just a guess, and it will depend on who you talk to at Smyria)