To obtain Larvesta and subsequently it's evolution Volcarona in Pokémon Go, the only way currently available is by hatching it from a 2km, 5km, or 10km Egg.
A couple of weeks ago, Niantic hosted the A Mystic Hero event on Pokémon Go, which saw trainers help Blanche and her trusty Lapras out in exchange for some sweet rewards. This time, it’s another leader, Spark from Team Instinct, whose looking for .