You can draw a lot of spells at the deep sea research facility, but I don't remember which ones.

Is everyone already at level 100? If not, then make sure you use your stat+ abilities on them to get extra stat points.

Fighting monsters is probably the best way to get your spells, if you can survive the fights xD Ultima Weapon should have some way to get ultima, I just don't remember if it's through drawing or by winning ultima stones.