Often collections of primary sources will be gathered and printed in books. You can search for these in the Brandel library catalog (just NPU's library) or in the I-Share catalog (university libraries throughout Illinois).
To search for primary sources in a library catalog, add a keyword for the type of source you're looking for to your search. For example, "letters" or "photographs." If you're not sure what types of primary sources might be out there, try search terms like "sources" or "documents."