Samba packages for AIX 5.2 and later can be found at Bill Jojo's site: 

    http://pware.hvcc.edu/

From the site's front page

    Welcome to pWare!

    Open Source software for IBM System p server (formerly pSeriesxi
    and RS/6000) machines running AIX 5.2 and higher. My name is Bill
    Jojo and I work at Hudson Valley Community College where we use
    a significant amount of Open Source software to manage our
    environment.