Both of the doors are booby trapped into this building. Be sure you take them before you destroy the shipments with thermite during the quest How Little We Know.
Gomorrah - sometimes 3 in poor condition can be found in the room with gun shipments.Camp McCarran - on top of a bed in the First Recon tent, where Sterling is.Camp McCarran - can be bought from Daniel Contreras.Caesar's Legion safehouse - one can be found in poor condition.Wrangler inside a very hard locked case.188 trading post - can be bought from the arms merchant after level 11.Ītomic Wrangler casino - one can be found on the top floor, first door of the Atomic.
Fallout Wikia lists the following locations for the sniper rifle:
