You can learn spells from other schools to add to your spellbook using training points earned in the game.
The first should come from the 'Meet the teachers' quest. Available after you open up Unicorn. Others come every 4 levels to the training point at level 20, then every 5 levels.
You can also earn them from Zeke searching for things in all the quest worlds (Smiths in WC, beetles in Krok, cats in MB, etc).
