For unity (and any game, film, music etc) project pretty much everyone simply uses subversion.
Git is for source control:
ie, when you have a source - i.e. software, i.e. a few tiny text files.
Git is for computer code files - i.e Text Files of C, Java, or any other text file computer language.
Whereas ...
Unity has almost no relationship to computer code files or indeed text files. It's more like making, say, a film or an enormous photoshop project.
(The entire raison d'etre of git is the "ability to work offline!" with computer code text files: that feature is utterly irrelevant to storing terabytes of textures, video, 3D models, enormous binary scene files, etc.)
It is trivial to get SVN repos, for example at xp-dev.com or any number of free or paid suppliers.
On your Mac the best subversion client is VersionsApp (unfortunately you have to pay for it). On your PC, everyone uses TortoiseSVN (free).
(Of course, on Mac you can just use the command line svn client, which is built-in to OSX since it's just unix.)
For games, video, modelling, 3D, film etc SVN is the industry standard.