I just started FFX for the first time about a week and a half ago so I don't know much about where to find stuff in the game. I'm currently in the Calm Lands but I want to go back for some stuff. My question is where can I go to get some more Lv. 4 key Spheres? Thanks.

Oh and I wouldn't mind knowing where to get the first 3 Lv. Spheres as well. Any help is greatly appreciated!