This trophy can only be obtained legitimately in Episode 5, though you can obtain it easily using cheats. If you are planning on getting it legitimately, I recommend you play on Piece of Cake and follow a secrets guide in order to find all the hidden weapons. Make sure to use your Mighty Foot in order to conserve ammo and this should unlock once you have all the weapons in the game.
However, for a much easier way to get this, press
to unlock the secrets menu and click "Give Everything". This will give you all weapons with all ammo and unlock the trophy instantly.