One of these weapons can be bought from the Quartermaster after recovering the prototype version. It is possible to purchase another from Dagger Squad inside Vault 0, but only before the fight begins. Once the owner of the gun equips it, it no longer appears on the barter menu.
Also found in a locker in Vault 0. This locker is found in the Power Generation Wing in the same room from which a swarm of scurry robots emerge; characters also have to crouch to enter it. Additionally, a very high Lockpick and/or an Electronic lock pick is required to open this locker.