Instructions
Travel to Goodsprings, the first area of the game. Go to the General Store and search the shelves. If there is no pressure cooker on any of the shelves, speak with Chet and ask to see his inventory. He may have one for sale. If he doesn't, go to Doc Mitchell's house and search his kitchen.
Travel to Nipton and search each kitchen in all of the houses. Check the shelves of the General Store in Nipton for a pressure cooker.
Travel to the White Glove Society Casino on the Strip. Go to the basement kitchen and search for a pressure cooker there.
Search any home or shack you come across while traveling the Wasteland and look in the kitchen. There are pressure cookers in Field's Shack, which is just southwest of Nellis Air Force Base, and Harper's Shack, which is east of the town of Primm, at the end of Primm's pass and near Dead Wind Cavern.
Speak with any caravan merchants, scavengers or traders you meet during your journey. Their stock is randomized and one of them may have a pressure cooker for sale.