Gift: Route 15
You won't find Porygon in the wild in this game — you get it as a gift.
Looking for Porygon2? It isn't found in the wild in this game — evolve Porygon.
For the look, the best colour match is Lure Ball or Great Ball.
Evolution: Porygon → Porygon2 → Porygon Z.
Porygon in every game · Pokémon Sun, Moon, Ultra Sun & Ultra Moon interactive map (Alola)