Several of the tutorials in 3D Photoshop include third-party models, cutouts, backgrounds and textures. The tutorials with downloadable assets are all clearly marked in the book; here's where you can download those files. You'll need to unZip the downloaded archives if your browser doesn't do this for you automatically.
* Models marked with an asterisk have been generously lent by the Digimation 3D Archive. You can find out more about this outstanding collection of 3D objects on their website.