Ext2 is extension 2 plugin for maya 2008
Well you can download my mirroring blend shapes tute from here at SM http://www.simplymaya.com/movie_page...tml?tut_id=157
Also the tools in the tool box option has reflections across axis tick box.
If you use zbrush you can mirror it on the fly or do one half and mirror symmetry as well even mask out what you dont need. Also subscribe to itunes they have a digital tutors podcast video for using the blendshape brush which is cool and it features how to do it as well