The files are located at:
http://mirror.centos.org/centos/4/csgfs/
Documentation for CS / GFS is with the other CentOS-4 docs at:
http://mirror.centos.org/centos/4/docs/
You can add the csgfs repository to your yum configuration by downloading the CentOS-csgfs.repo file and putting it in your /etc/yum.repos.d/ directory:
http://mirror.centos.org/centos/4/csgfs/CentOS-csgfs.repo
Installation instructions are provided in the above documentation link.