Go to the cave up from Mossdeep.There is an old man.Talk to him and he will ask you to get him 4 shoal salt and 4 shoal shells. Explore the cave in the morning(on the game)to find 4 shoal salt. Go back to the cave in the afternoon and it will be flooded. Explore and you will find 4 shoal shells. Shoal salt looks like brown dirt. Shoal shells look like a blue circle surrounded by white circles.