Mercy, unique Grenade Machinegun
Spoiler Dead Wind Cavern. Think Deathclaw Sanctuary from Fallout 3

AER-14. Unique Laser Rifle.
This Machine, unique rifle. Including it's model.
Spoiler Reward from an unmarked quest from Contredas or Carrie Boyd at Camp McCarran
The Humble Cudgel. Unique Lead Pipe. I'm not kidding :lmao:
Lucky. Unique .357 Magnum.
Gobi Campaign Scout Rifle
Spoiler Sniper's Nest, near Cottonwood Cove
Ratslayer. Unique Varmint Rifle.
Spoiler Broc Flower Cave, far south of Novac
Pew-Pew. Unique Laser Pistol.
Spoiler Reward for quest involving 50 star bottlecaps
CZ-57 Avenger. Unique Minigun.
Spoiler Devil's Throath, North-eastern corner of the map.
Dinner Bell. Unique hunting shotgun.
Spoiler Quest reward for Bleed Me Dry at The Thorn.