I do not use AIX nor ftps but I can make a few comments. A particular ftp program might have options for running over ssl. But you can not take just any ftp program and set a configuration option to transform it into an ftps program. It is possible that your AIX system has ftps capable ftp programs, but I would be a bit surprised if it does. You probably will need to get some software. You did not even reveal if you need client or server or both. Figure that out before you go looking for software.
ftps is still rather new and in its formative stages. Consequently there are various flavors of ftps. See
implicit ssl vs explicit ssl.
I have never used ftps, but on paper it looks really great! But that is how I feel about the Itanium chip too.
It is interesting that your mainframe is using ftps already. What does it connect to?