First off GNOME is another Desktop Environment, so you wouldn't be using it with the KDE gui rather, you would be using it instead
of KDE. But, if you look on your install discs, you probably have everything for a full GNOME install, so check there, that's your best option. You could always try and download the source from the download website
, but it would probably work the best, and be the easiest if you just installed from the distro CD you installed from.