A book in the Tulla library says that each colledge of magic once contained 8 spells. So you may be able to learn these. However my main idea is that new spells be introduced that you can enchant into items. I am not suggesting new colleges, just new spells. Spells can exist outside of the 16 colleges as is evidenced by scrolls of exiting or the banishment spell. However as you would not be able to sellect these spells from the regular menu I suggest that you must enchant items ie. a mage's staff with these spells. These spells would however be dependent upon your own mana stores, not an internal mana store of the enchanted item.