Where can you buy Cup of Lifenoodles in Earthbound?

You can't buy it anywhere. However, you can buy the Horn of Life in Saturn Valley for $1780, which does the exact same thing. The only difference between them is the price they sell for. You can find gift boxes or treasure chests containing the Cup of Lifenoodles in Peaceful Rest Valley, Talah Ramah's Cave, The Pyramid, Dungeon Man, Deep Darkness, Stonehenge base, and Lumine Hall.