Tickets for the Cure's show in Asunción, Paraguay are scheduled to go on sale at 10 AM today (check local time here). Good luck!
Also, a tip from Jay for any international fans still having trouble getting tickets - ask your hotel's concierge to buy them for you. Worked for him with the Bogota and Rio tickets.
Update (March 10th, 2013): From now until March 21st, if you buy 2 tickets in the same section, you get another 1 for free. (Thanks Maggie)