The Arcane university in center of the eye on the map for mage spells, The Half-way there Inn for sorcerer spells and bard spells, The pyramid in the south west and the necromancer tower (Skullzow I think) in the North East for Necromancy spells, the warlock cave in the South middle of the map I think has some spells (but it has monsters guarding it that are quite powerful so maybe hold off on that for a few levels). Tradeford I think also has one or two spells but I might be wrong on that.

Keep in mind spells are pretty expensive (i.e. 2000 gold for the level one tier and getting into 20,000 for the really high end stuff). This isn't a super big barrier since there are special main quests in the game that hit around level 20 that give a lot of gold. So just play as you want and good luck to you.