Yep. Wiz is right. If you there is a magazine about it, then there is a hungry niche. Even if you think it isn't.
A real niche I found at the magazines store was Parrots. Specifically, Parrot breeding, parrot care, and parrot training.
These were the 3 sub niches I dove into, and they turned out to be a gold mine.
Here's a list of some my favorite places to find niches:
1. ClickBank Marketplace
2. Amazon(most popular magazines and books)
3. Magazines.com
4. Ebay(Pulse, Popular)
5. Ebooks.com
6. Bookstore/Magazine store