Either buy a CD-ROM or download it from an FTP site. If you are getting it from an FTP site be sure to read the README.FTP or other documentation on the FTP site. It will detail eveything you need to get and how to set things up for installation. Basically you need to have an existing Linux system, and a free ext2 partition to put everything. You'll need to download rpps/*.ser and rpps/*.rpp for all the series you need, bootstrap/bootstrap.tar, config/*, bin/*, images/rootdisk.img and a rootdisk from images/*/*.img.