First you need to install Homebrew

Then you need to install GCC from XCode "command line tools"

  $ brew install gfortran umfpack swig
  $ sudo pip install  numpy Cheetah lxml scipy matplotlib
  $ brew tap ksnieck/homebrew-gnuradio
  $ cd /usr/local/Library/Taps/
  $ mv ksnieck-gnuradio/ titanous/homebrew-gnuradio
  $ brew install gnuradio
  $ brew install rtlsdr gr-osmosdr gr-baz --HEAD

There's like a shitton of dependency for GNURadio, you'll possibly need a fast Internet connection or wait.