Wikipedia is a great place to start if you're not sure who to choose! This article on Music and Politics can help you find important musicians and topics. Remember to be sure your musician has songs with words that you can analyze. For some examples of social justice songs, read this article on Protest Songs in the United States.
Most performers have a website. Remember to Google your performer and check out their webpage.
Finally, see if your performer has been inducted into the Rock Hall of Fame. There are many fabulous articles on their site, and some of them also have their own Rock Hall Research Guides!
Now that you've picked your performer, what do you want to know next? If you're feeling stuck, try this keyword brainstorming worksheet below.