The content of most if not all of the books and pamphlets is available at multiple places online. The best place to start, as with most things, is a google search. Many of the books are available in their original format scanned in via Google Books, or at archive.org at the Internet Archive. Project Gutenberg also has some scanned in images of original texts, and has the text versions of nearly every significant work in the public domain.
You can also find high quality images of original texts and other text versions of books from many government resources such as the US National Archives and the Library of Congress. There are an endless number of local and university libraries, historical societies and museums that have such materials as well.
What’s that? The public domain? Detailed rules for works that are in the public domain can be found here.
Why this information?
It is important to clarify that most of the materials I am producing come from the public domain, and it is not my intent to profit by creating the impression that the information I am selling is only available from a paid source. Many are online and able to be seen, read and printed for private use in their original format at no cost. This is due to the hard work of thousands of individuals and the painstaking care taken to keep books in a preserved condition for years so that we may all enjoy them.