Where can I find rare silent films?

I love silent movies, and I want to watch more with the actor Elmer Clifton, but the only ones that seem to be out of him are "Birth of a Nation" and "Intolerance." He made several movies with DW Griffith, including "Nina, the Flower Girl," "The Lily and the Rose," and "His Return." Do you know where I can watch these movies, or buy them somehow, if they've been released? Thanks!