You can use the library online catalog, OSCAR, to find published primary sources or books including primary documents. If you are interesting in the writings of a specific individual, just do an author search. If you are looking for primary sources on a specific topic, enter your keywords and add one of the following words, depending on what you are looking for: correspondence, papers, speeches, memoirs, personal narratives, documents, sources.
For example: Haitian revolution and documents
Abolitionis* and sources
Here are some collection of primary sources you can find in OSCAR:
Articles from the time period of the events you are researching are also primary sources. Consider these newspapers and archives for your topic.