im in act two in the city and have yet to find a long gun, no shotty, no automatic rifles.i rome and explore everywhere and check just about every box , bag and cabinet. where are the good guns? or as the old jack in the box commercial says : WHERE's THE BEEF?
The Melee Weapons are actually the best. You find them literally everywhere, and they don't need any ammo.
As for the guns, though, when you kill a Punk with one, you can pick his pistol/other weapon up. That's how far I got into the game before my save got deleted due to certain out-of-game events.
To actually answer your question of where the good guns are, I'd say you'll need to progress more in the game. I don't think it's gonna be just "Hey, you're in the city now! Here, have an RPG."