To obtain the Ventilator at the very beginning of the game without ever upgrading your lock picking skill, simply take dogmeat to vault 111 and the overseers office as soon as you get him. Once there, make certain the door to the ventilator room is open, then speak to dogmeat, choose the dialog options "fetch", then "Items" and - voila! Watch as he comically waltzed right up to the master locked case and plucked the ventilator right out, before dropping it on the floor at your feet! To get the ammo for it, however, you will have to "trade" it back from his inventory.