Audiobooking step 1: Find a book
Creating an audiobook from text has many, many possible uses. Verbalize accepts text from just about any source, so if you want it spoken, it can probably be done.
If you're looking for the full text of a book, the internet is your library, especially if you are happy with public domain books. There are also some sites that give you unlimited text access to books for a small fee. Here are some free sites (by no means an exhaustive list) to start with:
When acquiring text from any source, you need to be able to select the computer-readable text. When downloading, opt for plain text, rich text, PDF, HTML, Word DOC, Pages, or any other format your computer can open. Plain text, though, is preferable.