Mod:Fallout: The Frontier/Lysander XL

Locations
Snowblind Point, inside a lighthouse with an electric field. To enter you need to complete the main quest line. Upon completion of the main quest line on the last floor of the lighthouse (near Gaileon Particle Harbinger) the door to the developer room will be available, the weapon is on the table near Jack.

You can get to the developer room using the console command: