Non-repeatable
- Cerulean Cave (B1F, requires Rock Climb)
Repeatable
- Route 17 as a gift from Biker Reese if you have his phone number
- First prize in the Bug-Catching Contest after obtaining the National Pokedex
- Prize at the Pokeathlon Dome for 3000 points (Monday, Tuesday, Thursday, Friday, Saturday)
Dusk Stone (Bulbapedia)