The AN/PEQ-2A is available in the mission "Stronghold" equipped on the starting MP5. It is also present on various weapons in Special Ops.
Also, when enabling Console commands (only on PC), it is possible to activate laser both in Singleplayer and Multiplayer. On Akimbo weapons, there will be two laser beams. It also appears in the special ops mission "Iron Clad" on solo, to mark targets for the tank.
Call of Duty: Ghosts
The AN/PEQ-2A is seen in the level "Clockwork", where many of the Ghosts have it attached to their weapons. The player, however, does not have it.
Call of Duty: Modern Warfare 3
In the Stronghold, while equipped on Yuri's MP5, the AN/PEQ-2A appears much smaller than in previous games.