WorldCat, can be used to identify primary sources using the strategies outlined below. Note that the results will be a mix of online resources and print resources.
You can often find primary sources by adding words like sources, biography (which is used to describe autobiography as well as third-person biography), letters, correspondence, personal narratives, diaries, writings, or archives to a search.
For example, a search using the terms Black Panther Party biography turns up numerous memoirs and autobiographical memoirs by members.
Another good way to find primary sources in WorldCat is to use the advanced search and limit by publication date. You can thus find titles contemporary with an event or subject of interest.
Example: to find publications about the Black Arts Movement appearing in the 1970s, type Black Arts Movement in the search box and limit publication dates 1970-1980.