At any level before the stage where you have to kill General Tatarin, go to the rebel base. Go in circles around it to find a machine gun that has 3600 rounds.
Cheat List
Enter the following while playing the game.
Code - Effect
Y, A, B, X, X, R - shotgun
Y, A, B, X, X, LEFT - invisibility
Y, A, B, X, X, RIGHT - slow motion
Y, A, B, X, X, DOWN - fast motion
Y, A, B, X, A, R - change spawn point
Y, A, B, X, A, RIGHT - infinite ammo
Y, A, B, X, A, DOWN - max charisma
Y, A, B, X, A, LEFT - nail gun
Y, A, B, X, Y, R - sub machine gun
Y, A, B, X, Y, RIGHT - sniper rifle
Y, A, B, X, Y, LEFT - rocket launcher
Y, A, B, X, Y, DOWN- heavy machine gun
Y, A, B, X, B, R - ragdolls
Hair Length
While playing the game, notice that Chris' hair gets longer with every mission.
Unlock Liberty Island
To unlock the extra stage, Liberty Island, just beat the game on any difficulty.