www.bhphotovideo.com also has it, and the upgrade edition.
And just for reference for other folks, or in case someone suggests downgrading Windows 8: http://support.microsoft.com/kb/2832566
That article indicates something that I wasn't fully aware of - only copies of Win8 that were actually installed and delivered by an OEM pre-installed have downgrade rights. I thought that you could buy a windows 8 system builder license and use that to downgrade, but that is not the case. There is no retail version of Windows 8 that comes with downgrade rights.