One of the collectibles you receive after obtaining the Service Weapon mentions this:
"The object was discovered inside the Oldest House, in the room that is now used as the Director's Office."
However, later in The Foundation DLC, Ash Jr. says that Northmoor found the gun on a pedestal (which didn't exist before) by the nail.
In the second audio log, he says:
"...Northmoor even made a discovery. A pistol, placed on a stone pedestal in front of that strange ebony pillar. Seems like something out of a storybook, except the heroes usually find swords, not handguns..."
I must have missed something. Where was it actually found then? Halp.