In addition to the databases and websites below, you might also wish to try Tutt Library's Primary Sources Online guide.
You can find printed collections of primary sources in the catalog by searching for the keyword "sources" along with your subject keywords (i.e. "slavery" or "abolition"). Try this link for those items in the catalog with the subject Slavery -- United States -- History -- Sources.
PBS Slavery and the Making of America,
Brown University Library Center for Digital Scholarship
African American Sheet Music Collection https://library.brown.edu/cds/sheetmusic/afam/index.html
Amistad Research Center