You need the teleporter stones to get a treasure cave containing the level 6 BF key. You can use either the teleporter stones or a spell to swap places with a creature in a lava surrounded section of teleporter island to get to a level 1 BF key, though you can also just skip it since you will most likely have found other keys before getting there.
There is some loot in the treasure cave, but I don't think there is anything essential you need the teleporter stones for. I should be posting a procedure soon for hex editing character positions, which would give you another way to get to the cave.
