i can help you, im from Argentina, i both my tickets yesterday, but there is no good tickets now, the best tickets has been sold out, and you need a VISA credit card, just let me know...
Try calling to (54 11) 5237-7200 this is ticketek (is as ticketmaster in USA), they are selling the tkt for BA shows. They have an automatic answer machine and there is an option to speak in english If you want a very good seat, I recommend you to buy "San Martin seats" sector "C" or sector "D", about U$ 95 per seat
Do we have news or a trend about how fast the tickets are selling right now ? It may be an indicator for the european leg or other South-America expected shows.