Route 210 > South of the pit between the climbable rocks (requires Rock Climb) (hidden)
Route 228 > At the end of a narrow bridge south of the pair of Pokémon Rangers
Iron Island > In the last room
Pokemon with the ability Pickup Between Levels 41-60 a 4% chance to find one. Between the levels of 61-100 a 10% chance to find one.
Source: Bulbapedia pages
