Ice beam, Go a bit south from slateport, and then head west. Keep going until you find a ship. Go on and you'll show up on the side. Go inside and follow the ladders and go in all the cabins and beat all the trainers. Not too later, there will be a cabin with a captain person with a white coat. Near him is the storage key, take it! Next go to the door that was locked, and go in with the key. It's in there.
