You will find it here: http://xquartz.macosforge.org/landing/
Once you have that installed, the official Mac OS X download bundle will work fine.
If not, and you get an error saying:
Then you will need to do this:"Spring_XX.0" can't be opened because it is from an unidentified developer
1. Open up System Preferences
2. Go to "Security & Privacy"
3. Click on the "General" tab
4. If necessary, unlock the panel to make changes (click the lock in the bottom-left corner and then enter your account password when prompted)
5. Under "Allow applications downloaded from:" click "Anywhere"
Then you should be good to go :)
Oh, and once you've run Spring at least once, you can reset your "Allow applications downloaded from:" setting to a more restrictive option and Spring will still run. Once it is authorized it looks to be permanently so.
Belmakor