The following is a list by level of all the weapons and where to find them. Note: The first and last level do not count for getting weapons. To get a weapon to keep for later use, keep it in your inventory at the end of the level. This is also useful with the "Easy Weapons" hint. These are all done under Agent mode.

Datacore: Demolition

P9P (Pistol):
You start with this gun.

Nightclub: Stakeout

Falcon (Pistol):
Found from almost any guards, such as the first two.

UGL Liberator (SMG):
Found from the guard on the third floor. He should have two of them.

DEF-12 Shotgun (Close Combat):
Find from the enforcer in the beginning (After you scan him of course!)

Frag Grenade:
Hidden behind a vent in the basement. The stairs leading down are located in the back right corner of the nightclub from the front door. Once you have gone down the stairs there should be two vent coverings. Break them and get the grenade.

Subway: Retrieval

DW-P5 (SMG):
Found in the only open storage crate after you have gone through the parking garage.

CMP-150 (SMG):
Found from some guards.

Rooftops: Escape

M60 (Heavy):
Found once you get to the fire doors. Go past the fire doors and lock pick the door. It should be standing atop an artillery box next to the guard.

Jackal (Heavy):
Found from the sniper if you did not shoot it off the building. The easiest way is to put away any weapon you have (Up ) and use disarm (RB ).

Mansion: Infiltration

Magsec 4 (Pistol):
Found from all guards at the beginning of the level.

Viblade (Close Combat):
Found once you get in the mansion. It is standing on a pedestal in the middle of the laser maze.

Laboratory: Rescue

Magnum (Pistol):
Found from the yellow suited guards that come once the alarm is triggered.

KSI-74 (Assault):
Found from almost all blue guards.

River: Extraction

Rocket Launcher (Heavy):
Difficult to get and should only be done on co-op. Once you get outside, open the gate and clear the guards. Now on the hovercraft that you take, once on the gunner press Y to switch for another heavy weapon (M60 and Plasma Rifle only).

Trinity: Infiltration

Combat Shield (Close Combat):
Found from one of the guards after you picked up Dr. Carrol. There are two guards once you find the round walkway the leads to the lower level.

Hawk Boomerang (Thrown):
Found in one of the boxes in the beginning of the level. This is easier to get after you have picked up the X-Ray goggles in the weapon cases to the left once you start.

Trinity: Escape

Psychosis Gun (Pistol):
Found from most scientists throughout the level.

Jungle: Storm

RCP-90 (SMG):
You can find this either from the assaulting guards or atop of boxes by the left wall. Try using this on that level every time you play. Secondary (RB ) makes an outline of red around your enemy, at the lost of some accuracy.

Temple: Surveillance

Plasma Rifle (Heavy):
Found at very end of level from any of the phantoms.

Laptop Gun (Assault):
Found from one of the two guards after you have gone down two levels. If one of the guards plants one, reprogram and pickup. It should say reprogram once you get close to it.

Frag Grenade (Thrown):
Found from some of the guards. This may be difficult to find.

Multimine (Thrown):
Found from the guard that is either on the water bridge, or around the corner after it.

Outpost: Rescue

FAC-16 (Assault):
Found in one of the weapon cases after you rescue Jonathan.

Flash Bang (Thrown):
Found from one of the guards in the room before you go through the double keypadded door.

Bridge: Assault

Shockwave (Heavy):
Found from the fallen Carrington sniper once you go to aide Jonathan's team.

Super Dragon (Assault):
You may have found this gun before. Found at this level from some of the guards on the bridge.