Amazon U.S doesn't ship a lot of stuff to Argentina. Rumors are that this is about to change but in the meantime your best bet are the Amazon stores in europe (co.uk, de, fr etc...) When searching try to find items that are "AmazonGlobal Eligible". Shipping is expensive it's sent by a courier but they handle everything with aduana (Amazon pre charges you the estimated tax) and you get your things in about 1 week straight to your door.
I did get one shipment from Singapur through regular mail but it's still a pretty Kafkian process and takes a very long time (about 30 days to get your stuff from the time they actually reach BA).