Which book are you referring to specifically? Typically, a book's example files can be found on the page where you purchased it. Underneath the buying options and Add to Cart buttons, you should see an "Essential Links" section. The first one down there usually is the link you will want to click on to get the files.
Also listed there are errata, a place to give feedback about the book and other useful links.
Some books content will be hosted elsewhere, and that will usually be indicated in the books preface.
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