See History: Primary Sources for a more complete list of available resources.
The resources listed here are not the only ones available. Many others are in print or microform and can be found by searching library catalogs, like CMU's library catalog, or Worldcat, a database of library holding thoughout the world (though mainly U. S.). Use some of these terms combined with your topic:
early works to 1800
"civil rights" and correspondence
slavery and "personal narratives"
Holocaust and "diaries"
"race relations" and interviews