Elem Pedras

Pedra of Wind: Harnella
Pedra of Flame: Zoshonel
Pedra of Earth: Berthe
Pedra of Water: Grueza

You will get one of these in the beginning of the game, depending on which one you choose. To find the others you will need to train a few times with Magnus (that's you) at a few locations. Those locations are Mylesia, Mount Ithaca, and Gules Hills. In each of these areas, after training a bunch of times you will run into a unit that consists of a high level dragon and a character. The character will either be a Dragoon or a Dragon Master. The Dragon will be very high leveled and hard to beat. Depending on what element the dragon is, is what element your new Pedra will be!

Pedra of Virtue: Ishtar
There is a man in Muji, at Gules Hills who is missing his daughter that he couldn't write to after the volmus mine area was liberated. Talk to him and he'll ask if you can find her. Then go to the Volmus mine and talk to the woman there, she'll tell you to go to Mount Ithaca. Then go to Mount Ithaca, to the town called Cactovich, and you'll find the mans daughter. She will then reward you with the Pedra of Virtue.

Pedra of Virtue: Ishtar
There is a little kid in the town of Jiram in the Highlands of Soathon. He had lost his dog in the war. If you take a Hell Hound to him, he'll thank you, and reward you with the Pedra of Bane, which he calls "A funny looking stone that he found in the forest". If you don't give him the dog the first time you enter the town, the next time you will talk to his mother. You will have to exit that level and come back.