Gift: Route 8
You won't find Omanyte in the wild in this game — you get it as a gift.
Looking for Omastar? It isn't found in the wild in this game — evolve Omanyte (Level 40).
For the look, the best colour match is Dive Ball or Quick Ball.
Evolution: Omanyte → Omastar (Level 40).
Omanyte in every game · Pokémon Sun, Moon, Ultra Sun & Ultra Moon interactive map (Alola)