Search the indicated location to find the corresponding unique weapon.

Blad-On-Stick (Trip Blade): In the Marauder Hideout, northwest of Edgewater. Kill the bandit leader to get it.
Maxwell (Impact Hammer): Sold for 3,000 bits at the Emerald Vale General Store.
Ol' Reliable (Light Machine Gun): In the Primal Nest, next to a dead body in the canyon area.
Shock Stick (Riot Baton): In the Geothermal Plant, carried by the security chief's corpse.