Look at the bibliographies, footnotes and reference lists in the articles, books, and reference sources you have already found!
These will lead you to other relevant sources, both secondary and primary sources. Then, search for the article or book in Knox Primo to see if it is available. Use Tipasa to obtain articles not available in full text in Knox Primo.
Artstor is a database of images of art work, art objects, cultural objects and architecture contributed by museums, archives and libraries from all over the world.