Ok, so I waited 4 days in the Y-12 and I waited an additional 3 outside. Still no luck. Upon further exploring (or, looking for more harnesses) I figured out that every creature respawns EXCEPT for the Harnesses.
Well, thanks to everyone who replied. My character is literally 20 XP from being Level 49, so I guess its time to move on to a new character. I'm going to miss the K9000, but you remember what the moral of Dead Money is, right?
If you're on the PC, you might try finding the skeleton with the gun and resurrecting him. Y'know, bringing up the dev console, clicking on him, and typing "resurrect." That might refresh his inventory. You'll have to kill him again to get it though.
Alternatively, you could just go player.additem xx00e39e, where xx is replaced by the mod index of OWB. I've got OWB after NV.esm, DM.esm, and HH.esm, so its mod index is 03.
This is all only on the PC, of course. If you're on the consoles, you're out of luck.