As long as your subscription is current, you ought to be able to see it on RHN. Go to https://rhn.redhat.com
and login, then go to "Channels" on the top bar, and then, on the left, there is a button that says "All" (Subset of "Software Channels") Click on that, and it will bring up all channels. Scroll down until you find the channel for the 64-bit ( Most likely "Red Hat Application Server 3.0 (AS for ia64)" or something like that) and you should be able to D/L the ISO's from there. Happy hunting.