Games : What spells can not be found as loot in Skyrim?

Yes, I'm aware that spell books are rare loot and if you want them all, it is more useful to buy them. But I don't want to - it is a roleplaying thing. I'm not a mage anyway and don't have the maciga for most of the spells, I want them all because I'm a hopeless idealist. And I don't mind that it will take time, Skyrim is still one of my favorite games and exploring and clearing new dungeons is what's fun, so having the possibilyty of finding a new spell adds to that. Therefore I do not want to buy even one spell that can be obtained otherwise. Which are the spells that never drop, even inside Black Books, and can only be obtained by buying them?