There are many websites sponsored by governments, museums, universities, and organizations that can provide many perspectives on your topic. The website examples listed here may not be directly about the book you are studying, but they offer information related to topics derived from the assigned books. There are many other possibilities. Make sure that you carefully evaluate any webpage that you decide to include in your project.
site:.gov "the pony express"
site:.org "mental illness"
site:.edu "Timothy Leary" AND LSD