Camp Golf, main resort building, ground floor. Turn right and go into the Ranger quarters, then left and into the kitchen/mess hall. There are two pressure cookers on the stove there. Taking them counts as stealing, so make sure none of the NCR see you. (You'll still get the karma hit).
Cant remember the name of the place but that shack along the road just south of the black dude who tells you how to get into Boomer territory had one in it..fields shack I think had a unique bb gun in it as well
I didn't have the patience to look for one. Fortunately, a programmer's magazine raised my science level to the point where I didn't have to. I'm assuming you're looking for one for Jack to fix the debreather for you.