If you haven't already visited the jobs page, then you should do so here:
Posting in this forum that you "are available" will achieve nothing, you need to chase the jobs up yourself.
Recruitment tends to take place mainly from January to about May/June for the following season. So recruitment to go South in the summer season 2011 / 2012 will take place from Jan - June 2011.
There may be a very few jobs come up after June for the coming season (i.e. from June 2011 for 2011/2012 season), if someone previously recruited is unable to go for instance, these are by their nature rare and unpredictable as to what job/s they may be.
There are recruitment fairs, see the jobs page and also recent posts in this forum. In the USA in particular attendance at a fair increases your chances of employment greatly.
Tenacity pays off - if you don't get the first job you go for, keep trying, it shows it's more than just a whim on your part.
Here's a really useful post
for US citizens from Alan Light who has wintered several times in Antarctica at McMurdo and also the South Pole station.