Raid police stations and gun stores. Alternatively, fire up Bedford Falls or Phoenix. Raid the police station, gun store, bunker, the armories in the mental asylum, and the military facilities. Trust me, you'll find ammo. From a realism perspective though, it makes sense that you won't find a lot of 5.7mm ammo. The Five-seveN pistol itself is pretty rare even among military/police, let alone civilians, and 5.7mm ammo is proprietary - only the FN Five-seveN and P90 use it. I'm not sure if ammunition is included in the mod makers rarity settings, but if I were you I would go with something more common like a 9mm or .45. Last point... Your average person can't aim for shit. It makes sense that huge amounts of ammo would get burned through during the zombie apocalypse, between fear/adrenaline, poor marksmanship, and the fact that (traditionally speaking) the only way to fully kill a zombie is with a head shot (which, by the way, is an incredibly small target made that much harder to hit by a zombie's erratic movements; any professional shooter is taught to aim for center mass, e.g. the chest, because small targets like the head and limbs are very hard to hit consistently and missing means you could hit an innocent bystander)... you do the math. I would love to see a mechanic for reloading your own ammo since I don't find a lot of ammo on zombies, but on maps with a lot of gun/ammo spawn points, it's really kind of pointless because you'll end up having more ammo than you know what to do with.