I assume you've tried Amazon for the 6? Also, try Amazon.co.jp (Japan - where the Elixir is called Maverick).
The Elixir 7 is just an upper update - basically the same midsole as the 6, but with the addition of Mizuno's flex controllers. Upper is a bit lower profile and sleeker, following the same trend as Inspire 8 and Nirvana 8.
Here's a summary:
http://www.runningwarehouse.com/video/index.html?video=MEL7M1
Edit: More here
http://www.runnersworld.com/article/0,7120,s6-240-400--14221-6-1X2X3X4X5X6X7-8,00.html
Edited: 29/02/2012 at 11:02