After endless hours of exploring I was only able to find 4 of the 6 terminals of the story, I finally found the actual body and duffle bag and then to my surprise the rifle isn't there but the holotape was, and then I read somewhere after massive frustration that it is known that it is possible that an NPC could actually take the gun.
However I did manage to find some sort of tazer gun along my exploration....seems very situational, like if a deathclaw got in close range of you while you didn't notice.