You cannot download it, because it is a fix for the bos.adt.lib package in AIX 5.1 ML01 which reached the end of its support cycle in 2006. For AIX 5.1 the latest maintenance level (ML09) plus a pack of post-ML09-support packages are available for download at Fix Central.
Without having checked it: most probably the fix is included in one of the post-ML01 maintenance levels and by installing these you don't have to worry about it.
I suppose you want to install Oracle 9 RAC, right? Install a better OS base in this case, you won't get any support for AIX 5.1.