Many sources have been published in books - these can include, but are not limited to:
To find books, Start with the UVic Libraries Books & Media catalogue. Add keywords like "Sources" "letters" "Diaries" etc. to find these kinds of sources.
If you don't find anything here, use Worldcat to find books in other libraries, and follow the links to interlibrary loan them.
You can also search for out of copyright books using the Internet Archive, or historical book collections such as:
We have many collections of primary sources in books, such as the one below - but sources may also be found inside regular books - to illustrate the author's ideas or provide documentation. Don't limit yourself to books with 'sources' in the subject headings!