How to find Moon Stones as well as Fire, Thunder, Water, Leaf, and Ice Stones in Pokémon: Let's Go, Pikachu! and Let's Go, Eevee!
In the Let's Go series of Pokémon games, certain Pokémon require the use of an evolution stone to help them evolve to their next form.
Moon Stones are one of the many types of stones available and are used to evolve a number of Pokémon in the game, including Clefairy, Nidorino, Nidorina, and Jigglypuff. So having a few of them in your inventory is vital to completing your Pokédex.
To get a Moon Stone, head to Mt. Moon and hope that your partner Pokémon, or the Pokémon following you, finds one hidden inside one of the many craters. There are only two Moon Stones available in your game per day, so be sure to choose the Pokemon you want to evolve wisely.
Basically, Pikachu or Eevee act as an item finder in Pokémon Let's Go. If they wag their tails quick, it means there is an item nearby. The quicker the tail, the closer the item is.
If Moon Stones aren't what you're after, however, you can head to the Department Store in Celadon City to grab every other stone for 5,000 Pokémon Dollars each. The stones will be located on the fourth floor of the building at Wiseman Gifts.