You'll find level 4 Spells, as well as Gysahl Greens and Magic Keys, in the Village of Gysahl. It's all expensive, but the real prize here is the Shuriken found in the Magic Key Shop. To find it, walk through the left wall one square above the exit door. Sure, it's one of the best Weapons in the game, but you can find (and buy) more and, more importantly no one will be able to use it until the end of the game. Unless you're overflowing with money, the 32,750 gil earned by selling it will help you more in the long run.