Forget the normal 'pretty parts stores'! You will need to get acquainted with the REAL parts suppliers that the commercial shops use. Find out where the local transmission rebuilders get their parts. Here in my part of the world, the transmission parts store only goes by the name TPS and doesn't advertise themselves. That keeps their customer base to mostly knowledgeable mechanics that KNOW who they are.
I would not worry about that planetary setup, it will keep going forever. Just put the 'soft parts' that come with a rebuild kit in and be SURE you replace the Torque Convertor with a DACCO rebuilt unit. If you just do that, you will come out 'ok' financially. If you start digging deeper, you might as well take it to a shop and get it done for you.