Many authors (especially those of classic literature) may have their works and personal papers in an archive. Some of these may be digitized and accessible through the Internet. It's worth doing a quick Google search to find an archive if available.
These archives will most likely be a .org or .edu, so limit your Google search by including: site:.edu OR site:.org in the search box. This will limit your results to sites with only one of those domains.
Always evaluate your sources - what Google considers to be scholarly may not be considered scholarly by your professor.