Go to passifidog town(you know , that town floating in the sea where you cant run). Now, walk down and go to the very right house and enter it. Then you see a man staring right out of the window. Talk to him. When he says:"I can't see Mirrage Island today", you have bad luck and have to try again an other day. But when he says that he can see mirrage Island, surf to the east and you should be there.