A good way to search for primary source documents is to enter "primary source" and search within government sites (.gov) or education sites (.edu). You can add words if you are looking for something specific such as "African American interviews", etc. Here is an example of finding primary source sites within education (.edu) sites: primary source site:*.edu (type those exact words and symbols with the word "site"). You can use quotes around "primary source" to search as a phrase.
Always be sure to evalute your web site for authority (who sponsors the site?), currency (when was it last updated or published?), objectivity (is it biased?), and purpose (is it published for education & scholarship, or are there other purposes, like commercial purposes, etc?)