The Breast Surgery International BSI is a collective Member Society of the International Society of Surgery ISS/SIC. Membership application for BSI therefore has to go through the application process of ISS/SIC membership. Do not forget to indicate in the ISS/SIC application process that you wish to become BSI member as well.
The Link below leads you to the Membership Directory of the International Society of Surgery which includes BSI members. To seek specifically for a BSI Member in your country, select your country and Collective Member Society BSI and submit your request.