The intended recipient of the package can give you the address you want: there is no standard and the path changes depending on the logistical support in force when you send the package.
Your return address in Antarctica is based on the logistical operation of mail in your research station. Your station manager can give you the proper return address for your mail.
The intended recipient of your package can give you the details you need. Depending on the vendor or military branch responsible for your recipient, the address will be different. There is no standard in a single season, and the address changes season to season.
The United States supports research on Antarctica to address questions about the health of planet earth. This is the charter of every nation that supports scientific research south of 60 degrees S, which includes Antarctica.
Many countries have research stations in Antarctica. If you don't know a specific person at a specific station, review the list of installations on the link below and you can address your correspondence to 'To Whom It May Concern' or 'Station Director'. Most personnel information for these sites are not published because for most, it is a temporary assignment. Your inquiry may be given more attention if you contact an installation belonging to your own country rather than a randomly selected station. Since there are no roads or street addresses, you can address your letter to: the station name, Antarctica.
There is no chamber of commerce for Antarctica.
The address for Amsterdam Centraal Station is : Stationsplein, 1012 AB Amsterdam
The web address of the Harlansburg Station is: http://www.harlansburgstation.com
The web address of the Fairfax Station Railroad Museum is: http://www.fairfax-station.org
The web address of the Woodlands Exploration Station is: http://www.woodlandschildrensmuseum.org
The web address of the Heritage Station Museum is: http://www.cityofdouglas.com
The web address of the Hedges Station Museum is: http://winfieldhistory.com
The web address of the Lisle Station Park is: http://www.lisleparkdistrict.org