There are still not enough bandoneon teachers available. Fortunately the number is increasing and there will be more in the future if you consider the actual number of students. Some bandoneonist do offer personal lessons. You may check the list of Tango and Bandoneon Musicians and search for the note also teacher in the section for your country. There are also some conservatories offering courses for bandoneon. Additionally it is possible to take lessons on-line via webcam.
Additionally there are many other conservatories in France ready to teach.
The Musician's Page
will list many bandoneonists with the remark also teacher
and who also give lessons.
Recently I was informed about an on-line teaching service. I do not know if it is effective and feedback is appreciated:
Ben Bogart (Currently in Argentina)
phone from the USA (800) 9-BEN-BOGart
rest of world: 1-617-407-6747
Argentina Phone: +54-9-11-6130-3038