SQL 2012 Mgmt studio x64 download can be found here:

http://download.microsoft.com/download/8/D/D/8DD7BDBA-CEF7-4D8E-8C16-D9F69527F909/ENU/x64/SQLManagementStudio_x64_ENU.exe

As found/listed at this link:

http://www.microsoft.com/en-us/download/details.aspx?id=29062