I don’t know that there’s any one source for an object that can produce unlimited amounts of food. After all, it’s something that would be valuable in any society ever. I’ve written before about the cornucopia, and mentioned in that post that I remember a story about a magic grinder.
This tale actually originated in Scandinavia, and the earliest known version is the Grottasöngr, which appears in some editions of the Poetic Edda. Basically, this story features a magic millstone that can produce food, and apparently other things as well. When King Frodi of Denmark overworks two slave girls, who are descended from mountain giants and were great warriors before being captured, they use the stone to produce an army to overthrow Frodi. Eventually, the stone and the mill break from overuse.
Later versions of the tale remove the army component, and seem to limit the grindstone to making food. The most common take involves two brothers, one rich and selfish and the other poor but generous. The rich brother offers the poor one some food, but then tells him to go to Hell. The poor brother, having promised he would fulfill the rich one’s condition, takes him literally and bargains with the Devil for the magic hand-mill.
In this variation, it isn’t the Devil who gives him the stone, but rather a wood-goblin. Regardless, the rich brother eventually learns the secret of the grinder from the poor one, but not how to stop it. Eventually, the grinder ends up on board a ship, and either the rich brother or the captain (depending on the version) tells it to make salt, but doesn’t know how to make it stop. So it ends up at the bottom of the ocean, and that’s why the sea is salty. The story is complete without this bit of folksy explanation, and I have to suspect it was tacked on, but the story tends to be called “Why the Sea Is Salt” anyway. While searching for information on the tale, I came across this Disney easy reader book, which has Minnie Mouse receiving the grinder from a dragon. It includes the theft of the grinder by someone who doesn’t know how to stop it, but not the bit about the creation of sea salt.