As a novice alteration spell, it should be pretty easy to find. Try seeing if any court mage is selling it. You can also easily loot spell tomes from mages and spell-casting bandits. There's the chance they can randomly spawn in chests, and if you've gotten most of the way through the College of Winterhold questline, you can get it from the Labyrinthian Chasm (You could also probably buy it from one of them).