
Upgrade lies on the ground in one of the sanctuary's rooms (main quest Priority: Horizon). Upgrade lies on the chest found after the third battle with Cerberus soldiers (secondary quest Tuchanka: Bomb). Upgrade lies on the desk nearby the second control point (main quest Priority: Sur'Kesk). In the shop Aegohr Munition (Citadel: Presidium Commons). If you don't see the weapon mod on the store's list make sure that you don't already have all of them or try visiting the same store later in the campaign (after completing one or more main quests). Notice! The stores always offer better versions of upgrades, so for example if you have Assault Rifle Extended Barrel I and you'll purchase the same upgrade from the store you'll automatically transform your modification into Assault Rifle Extended Barrel II. The last column of the table explains how you can receive/find/buy a certain weapon mod. In the multiplayer mode (Galaxy at War) the only way to obtain new upgrades is to keep purchasing crates with random equipment, hoping for good luck. Notice! The table seen below is only about the weapon mods you may find during the singleplayer campaign.

It's worth adding that if you've found a new upgrade of the same kind you won't have to use the modification station again, because it's going to be improved automatically. The game will always inform you what you can expect by installing a certain upgrade and you'll also see the difference on five bars that are about the weapon's properties.
