You can download a Kindle firmware .bin file from Amazon, use Kindletool to unpack it (you can download Kindletool from
Snapshots of NiLuJe's hacks ), then use 7Zip to open the extracted rootfs.img.gz and dig down to rootfs.img.gz/fwo_rootfs.img/usr/share/blanket/screensaver/ You'll find the .png images for the screensaver there.
Edit: Modified slashes to attempt to remove extraneous inserted spaces.