How to get Lightning Rod Soul Gem
First of all, in order to get this, you have to unlock the Stone Town level(the level were you get the eternal earth source). Make your way through the level by fighting off the enemies. After you make it past the part were you push the turtles, you will come up to a locked gate. DO NOT GO IN! Instead, after fighting off the chompies and the earth spell punk, there is a little hut on the left side of the entrance. Destroy that and the soul gem will pop out from under it.