Where is it purchased, and how would I get there?

+How does it compare to the TEC?  

Ap9?? I dont know of an ap9 but i think you mean ap7, there have been posts like this but anyway near bottom left of the northisland on the beach there should be an egg role shack, if you search around to the right of it on the water there should be something saying *Deep Water* go around near that sign and duck underwater eventually youll be in an underrground cave, simply swim out of it the youll be inside where you can buy ap7s and magnum, tec9 is better though but ap7s are still good  

I am assuming you are talking about the AP0. It is below the west hospital.  

Or that, two ap weapons but to be more specific the shop below mercy easy hospital that used to be the gun upgrade shop. (also where you buy mk23 and aug)  

I got the info I needed from some random dude (lol) It was the AP7, but thanks anyway guys.