Where can I buy Windows 8 if it says "region unavailable"?

I live in Bolivia and I'm trying to buy Windows 8 and install it on my custom built machine. The links I found on the official page, by following the Buy button, just makes me download a .exe file to upgrade.

I cannot upgrade, I'm not running a legitimate version of Windows 7.

Where the hell can I just buy the damn thing? Why is Microsoft making things so incredibly difficult for customers?

Can any kind hacker help me out? :)

Thanks! I can't wait to starting making some Windows 8 applications.