I recommend a local library. There are plenty of books on
LGBT history out there. I recently had to do a report on gay rights and marriage, and I found some fantastic books.
Gay Rights - Kafka, Tina
Gay Marriage - Friedman, Lauri S.
Homosexuality: Opposing Viewpoints - Dudley, William
I'm sure there are more, but those are some titles I used in my project. Good luck searching.
Edit:
Oh, and take a look at the "
LGBT Resources" sticky. It's bound to have something you can use as well.