See if you qualify for a free OS X Mountain Lion upgrade. - Apple.
Mac App Store - OS X Mountain Lion - iTunes - Apple.
If you bought a new Mac on or after 11 June 2012 that doesn't include OS X.
With the Mac App Store built into OS X Mountain Lion, getting the apps you.

Mountain Lion for Developers - Apple Developer.

Apple - OS X Mountain Lion - Move your Mac even further ahead.

apple mac os x mountain lion download

apple mac os x mountain lion download

OS X Mountain Lion - Wikipedia, the free encyclopedia.

30 Nov 2012. Learn how to get software updates for OS X and apps from the Mac App Store. In Mountain Lion, use Mac App Store for OS X Updates.
Apple - Support - OS X Mountain Lion - Get Started.