WMV loads all of the MPQ archives from your WoW client. You can also edit Config.ini to load additional patches to show .m2 files from WoD on v0.7.6, for example.
If you cannot see a particular .m2 it is because the object either does not exist other than as part of a .wmo, or your client is incomplete. Check your configuration settings to be sure that every MPQ is loading on startup. If not, delete userSettings folder and select your WMV directory again or add the missing MPQs to Config.ini.