There has been much debate lately (on forums, fan blogs, facebook groups etc) as to whether KStew's glasses are prescription or purely "ironic".
The style KStew wears is: MORGAN in BLACK/TORTOISE (unisex)- (You can tell from the photos below) . You can also get Morgan in all black and/ or all tortoise.
They are approximately $95 (made to order- ie come with prescription lenses) and they do ship internationally for about $20- $40 depending on where you live.
HERE IS THE LINK TO LOOKMATIC: http://www.lookmatic.com/morgan-black-tortoise