I bought a new MBA the week it came out and could not find a case. While I was in San Fran, I stumbled on these guys. Great case, semi-custom made. Great service and great protection. I would buy from them again. Here is their website and options you can chose.
http://www.sfbags.com/products/sleevecases/sleevecases.php
http://www.sfbags.com/products/sleevecases/sleevecases.php