You get a lot of them on the map, especially later in the game, also in Ellinia there's like a garden of magic crystals somehere and if you summon the turtle to help you fight the shaman, it gives you a ton of them also. I think you can also buy them at the dwarf castle (the one near the entrance to underground sea) but they come at an outrageous price. Don't waste them on items or wishing wells (uless they give a good item in return) in the future, it's not like they grow on trees.
