All files are in the TH3D Unified Firmware or you can download just the TH3D Ardunio IDE Installer here: https://www.th3dstudio.com/downloads/TH3D Arduino IDE.dmg
Thank you to http://designed79.co.uk for making the automated installer for our OS X users.
NOTE: If you are getting errors compiling for a printer with the 2560 board in it go to Tools > Boards > Board Manager. Look for ATmega2560 & revert to 1.6.21. Some users reported issues on Mac OS X with the latest 2560 board library.