When you have defeated the elite four you have a task to find the six sages. One of the
seven sages are in the relic castle after you find him there will be a room to enter
inside volcarona will be waiting for yoou.if you wanna watch you tube please

After defeating the elite four, n and ghetsis, you will be visisted by looker (pokemon
platinum) who will request for you to find the 6 sages (7 if you count ghetsis). One of
them will be hiding in the relic castle's second last room. He will give a tm. In the next
room, there is volcarona at the far end of the room.