If a book exists in PDF on the web somewhere, I estimate a 90% of chance of finding it by at least one of the following four methods, which altogether take only a few minutes if you're practiced at it:

1. Search library.nu. (You'll have to sign up for a free account the first time.)
2. Search Library Genesis.
3. Search Scrapetorrent.
4. Use a custom Google search and keeping clicking through links until you find a filesharing site link for the book - one that isn't broken yet.