Well, you could still try calling Apple's Latin America support branch; they may not have much presence, but they must have SOMETHING, since they do sell to that part of the world--if you explain that you've lost your install discs, perhaps they'll sell you a replacement, since your computer is still under warranty.
You can enter the serial number into Apple's support page to confirm it's still under warranty (obviously it IS, since the computer hasn't existed for more than a year), and if it's not registered go ahead and register it in your name to be thorough.
Alternately, there's always eBay:
http://cgi.ebay.com/APPLE-INTEL-IMA...ryZ80258QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
...this is $26 and claims worldwide shipping. A retail copy of Tiger will NOT do you any good, as said, because it won't boot Intel Macs--they all shipped with Tiger anyway.
Before you do any of the above, I'd give the mini install discs you have a shot; even if they won't actually install on the Mac, if they'll at least boot it to the point that it'll refuse to install, you should be able to use the password reset utility. Here's the Apple article on the topic (password reset stuff is down at the bottom):
http://docs.info.apple.com/article.html?artnum=106156
Alternately, if it refuses to boot from the mini restore disc, you can try to get somebody to LOAN you a set of Intel iMac install discs, with which you can do the above password reset or just a clean install. You don't even need to keep them, though I assume it'd be easy enough (and perfectly legitimate) to make a copy while you had them.
