The single best way to identify relevant primary source material is to read widely in the secondary literature on your topic; scrutinize the notes and bibliography for published primary sources that you can access.

Five College Library Catalog

As you search in the online catalog, watch for the words "personal narratives," "diaries," "interviews," "correspondence," "pamphlets," and "sources" as part of the subject headings; these may point you to published primary sources in the library collections.

You can also search for these words, for example, "el salvador" and "civil war" and ( sources or correspondence or diaries or interviews or pamphlets or personal narratives )

Other clues may be buried in the title, authorship, date of publication, etc.