Collections of letters, speeches, papers, etc. are available for many of the prominent individuals involved in the American Civil Rights Movement. To identify these materials in Knox Primo which have been published in book form use the person's name and select the "as author/creator" option:
The same search method can be used to find primary sources from particular organizations -- use the organization name as the search term.
Some full texts of Martin Luther King, Jr. Papers are available in the Online King Records Access (OKRA) Database.
The first seven volumes of the collection of King papers is also available in print form in Seymour Library: Main Stacks E185.97 K5 A2 1992.
There are some collections of oral history material on the internet done by reputable archives, libraries and other cultural institutions. Some good collections are listed below.