Using secondary publications of primary documents is never preferred, but is sometimes all that is available to the undergraduate researcher in a reasonable amount of time (someday you may have the time to visit Bancroft Library at UCal/Berkeley to see the Free Speech Movement papers, but not likely this semester). Note that searching the HELIN Catalog for subject headings that include the word "Sources" usually retrieves material that includes republished primary source documents, i.e.:
United States - History -- 1961 - 1969 -- Sources
United States - Politics and government -- 1945 - 1989 -- Sources
United States - Politics and government -- 1963 - 1969 -- Sources
United States - Social Conditions -- 1960 - 1980 - Sources