Academic library catalogs primarily use "Library of Congress Subject Headings" to describe books and holdings. Certain words which are official LC subject terms are often used for publications that contain primary sources.
Good terms to consider when searching a "library catalog" for primary sources:
Example searches in OneSearch:
Any field contains Abigail Adams
AND Subject contains sources
Any field contains Wounded Knee
AND Subject contains letters OR diaries OR correspondence
Any field contains Vietnam War
AND Subject contains "oral history" OR "personal narrative"