There are so many places outside of ClickBank, CJ, and CPA networks to find products to promote. Many companies have their own in-house affiliate programs that you would never find unless you looked for them. Also, a lot of companies do not even let you know that they have an affiliate program until after you become a customer.
If you want to find a particular affiliate program in your niche, just search Google for "keyword"+"affiliate" or "keyword"+"affiliate program", you get the idea.