Just copy the files in your plugin directory -> Applications/Maxon/CINEMA 4D R1x/Plugins
To be on the safe side, change the permissions of the folder.
Download Links:-
Laubwerk_SurfaceSpread_1.0.44_C4D_-_MacOSX.rar
Mirror :-
Laubwerk SurfaceSpread 1.0.44 C4D – MacOSX.rar
Mirror :-
http://nitroflare.com/view/26310E20DB53D83/Laubwerk_SurfaceSpread_1.0.44_C4D_-_MacOSX.rar