Primary sources are documents or objects created by participants or witnesses at the time of an event.
Examples of primary sources: diaries, interviews, autobiographies, government documents, speeches, photographs, and artifacts, such as pottery.
In Google, search for "primary sources" and your topic.
You could also try "primary documents" or "digital collection" or "digital library" in addition to "primary sources".
Use words that would have been used during the time period you're researching. For example, African American was not always used. The language in documents in previous times may have included Negro or black.