The first stardust stone is in the weapons shop. It's located in the spear holder. The second stardust stone is located in the castle. Its is in the room where you find the guard practicing on a dummy. Walk upwards along the stables with the horse in them and come to the stove were the blacksmith is. Turn towards the stove and press X. He will say something like "Ouch" but then it will say (Acquired Stardust).