I've heard that Volcarona is a near legendary pokemon, but where is it!!!
At the end of Relic Castle, there is a Turnback Cave-like labyrinth. Just always go down and left and you should find it easily. Level 70, so be prepared
You can also get it another way .
On route 18 there is a house ,in the house talk to the guy in the red suit and hat and he will offer you an egg . The egg after hatching will be a level.1 larvesta i.e. the pre-evolution of volcarona .
Hope I helped.