Gift: Route 8
You won't find Tirtouga in the wild in this game — you get it as a gift.
Looking for Carracosta? It isn't found in the wild in this game — evolve Tirtouga (Level 37).
For the look, the best colour match is Dive Ball or Net Ball.
Evolution: Tirtouga → Carracosta (Level 37).
Tirtouga in every game · Pokémon Sun, Moon, Ultra Sun & Ultra Moon interactive map (Alola)