The Sun Stone is an item that is a part of the Evolution Stones. It was introduced in Generation II as an item to evolve Gloom into Bellossom and Sunkern into Sunflora. Later in the Generation V games, it evolves Cottonee into Whimsicott and Petilil into Lilligant.
In the Johto region games, this item is located as a prize in the Bug-Catching Contest in Generation II or in Volcano Path , by a Camper on Route 13, or at the Pokéathlon Dome on Mondays, Fridays, and Sundays in Pokémon HeartGold and SoulSilver. In the Hoenn region games, this item can be found in Mossdeep City or may be held by wild Solrock. In Pokémon FireRed and LeafGreen, this item is found in Ruin Valley. In the Sinnoh region games, this item is found in the Underground, Valor Lakefront, or may be held by wild Solrock. In the Unova region games, this item can be found in Relic Castle, Nimbasa City, Dust Clouds, or bought in Black City. They can also be found via the Pickup ability.