You need to be strategic to find primary sources!
1. Keep an eye out for mentions of specific primary sources (letters, diaries, contemporary criticism, or other important texts) as you conduct your background research. Example - in the Benezit Dictionary of Artists, I read that the artist Michelangelo wrote poems towards the end of his life - perhaps there is a volume of these poems published? How can I check?
2. Conduct library catalog searches (Books / Media tab on library homepage). Example Searches:
3. Use bibliographies. You can use bibliographies you find in dictionary and encyclopedia entries (Benezit is a great example) to scour for mentions of primary sources. You can do the same with books and journal articles. You can use the database Bibliography of the History of Art to search for publications on an artist. These will only be references. You will need to do a search for the full text in the following ways:
4. Venture out into the web. Be sure to EVALUATE the sources you use. These days, there are a great many museums and cultural institutions that are digitizing archival documents, such as artist's letters. You can find some great free online resources by googling a keyword and "primary sources".
5. Contact a librarian for help!
This short video will give you an overview of what primary sources are and how they are different than secondary sources.