Well im currently doing all of the campanion quests and i am now doing veronicas quest, and there is a point were she asks you to help her prove to macnamara that the BoS are gona die so she gives you three options:
-find a gun from that vaut armory
-find out about helios one (archamidies)
- and somthing else but i cant remember what :/

So i told her that helios was not a problem which left me with the other two options so i said lets go and get the gun from that vault armory, i have already been to the vault armory so i whent back to find this gun and it wasnt there so i thought maybe its in my inventory... It wasnt, so i checked out the quest objective and it told me to get the gun if it still exists so then maybe i thought i could speak to her and tell her it doesnt exist...no i couldnt, so then i thought maybe i sold it and it wasnt so long ago i found the armory so maybe i can still buy it back and the only place i buy and sell from is silver rush and gun runners... Niether had it what do i do know? Please help?

Its in a very hard locked footlocker, if your lockpicks not high enough then you can get a key to it out of a locker in Pearls house at Nellis AFB. You should actually have another quest marker that should lead you right to it.

The footlocker is empty

Well, then it sounds like you picked it up and either sold it or stored it somewhere. If you sold it, then you're [censored]. If it's stored in your base or something, you might not be.

Because if it's not in that footlocker, then you(the player) or one of your companions picked it up. If you sold it, you'll have to find another way to finish the quest.

Since you said ARCHIMEDES II wasn't a problem, you could try there. Or just talk to Veronica.

-Nukeknockout

Sounds like you sold it without knowing it's value.
A quest marker should be there when the quest is active.
But that vaults a b**ch to get round. Not worth your time.

Do ACHIMEDESII if you can. The easiest of the options and does'nt involve vaults.
And it's actually useful as a weapon.

Or do the farming one, if you can.

I hate Veronica, never used her.

-Cheers