Automatic box problem

Hello .. my query is the following .. I have a Pontiac Vibe 2003 4x4 that is bad, according to the mechanic, the planetary gears of the transmission box ... I would like someone to give me some recommendation or advice that if it is possible to find only that piece of the box or if I have to change the full box .. or if they have any idea where I can get something like that ... I am from Honduras ... I appreciate your time and collaboration ..