From Bulbapedia, the community-driven Pokémon encyclopedia.
Three Isle Port is a relatively small area on Kin Island. It is also the only point in the Sevii Islands that holds the dock for the Seagallop Ferries that is not a city, aside from the city-less Birth Island and Navel Rock. It is also the first place players can catch any Generation II Pokémon in FireRed and LeafGreen.
*Dunsparce can only found after defeating the Pokémon League.