I'm having troubles finding the invisibility spell tome at all. I have Illusion at level 90 and I went to the illusion trainer in the College of Winterhold and he wasn't selling it either. I have checked all over the internet and I coudn't find anything else on how to get it, so where am I supposed to find it? I'd like to know where to buy it as it seems nobody is selling it.
The reason I'm asking is that I'm playing as a Dark Elf illusion thief, but the twist is I can't use weapons so I need invisibility.