If you still need lvl 4 spheres you can fight the land worms in sin, but they drop them kinda rarely. For a sure thing bribe the chimera brain in Calm lands for 196,000 for x2 lvl 4 spheres.
You can fight the mimic boxes in the omega ruins for 100,000+ a pop if someone has gillionaire. If not, then it's 50,000 I think.
I got too frustrated with not being able to find enough spheres so I gave up the sphere grid and just finished the game. It was so easy I'm so glad I didn't waste my time trying to level up so much.
