On the page i told you look down to the "Support" section. In this the first subsection ins named
"AIX software downloads from IBM".
In this the third line reads
"AIX Downloads on the IBM download page, includes trial software"
and "AIX Downloads" is a link guiding you to the download center.
Alternatively you can use the "search" function on the IBM webpage to find the download site. Put in there your OS version, fix level and your desired package.
bakunin