There was a "which cd" utility floating around, but we tend to put a redhat directory somewhere on the lan, which contains all the packages from all the CDs - in a pinch you could get a listing from ftp.redhat.com...
But if you mean, "available" as in "available for Red Hat from any source, anywhere", that is a bit more tricky.
One poster mentioned rpmfind, a good way to find packages - I also like freshrpms, and to some degree, fedora.us.
Sometimes google is the best answer however.
Joe
