I feel like a bad Bamon fan for not knowing this, but in which book does Damon say "there aren't 2 like her" about Bonnie?

Don't worry.. the books are really complicated..
He said it in Nightfall (5) when he was talking with Shinishi about her... the rest you can find it reading the book.. this books is the best of bamon until now (Midnight (7) will be better).. you can find it and download it free in internet..
Hope that this help you... goodbye!