A list of locations from the Fallout Wiki:
- Two in Roy Phillips's "bedroom" in Warrington Station, but they cost karma.
- Two each in the Personnel Offices and the CO's Quarters at Fort Constantine.
- All houses in Minefield have multiple pressure cookers in them.
- In a storage room at the Super-Duper Mart.
- In various houses in Megaton.
- Silver's house in Springvale.
- In kitchen areas of Springvale School.
- Tenpenny Towers storage (generator/metrostation room) on a shelf.
- County Sewer Mainline in Gallo's Storage Closet.
- Regulator HQ
- Our Lady of Hope Hospital
- Abandoned Shack at Clifftop Shacks
They can also be bought from merchants, if one is available.