The only Adept destruction spell I have right now is Fireball and that was the only destruction spell besides the cloaks I could find. I bought them from Farengar in Whiterun but I can't find the others.

College of winterhold is best place to look. Speak to Faralda.

Where can I find her? I can only find Nirya.

She likes to sit in the living areas on the right side of the entrance to the COW, she spends most of her time sleeping or sitting in a chair in her quarters.
EDIT in the hall of Continence.