To get to the dark ore mine, you need to get a force gem from Ferrus. Sooner or later, he'll send you a letter which shows that he got lost in the Fire Realm. Give him a ride and he'll want to go to Ocean Temple. Go there and he'll give you a force gem, which will open up the path to the Dark Ore Mine.Once you have gotten 10 dark ore, go ssouth, and you'll be confronted by a rocktite and some other little ones. You'll need to survive with at least 9 units of ore. Once in the Sand bit of the Oceam Realm, go left (East) to a warp gate. Warp, then go west, south, then east to another warp gate. Warp there, and you'll be close to the trading post.