Many websites offer pre-made "OS X Mountain Lion ISO" files. Downloading and using these carries significant risks:
Apple now provides the Mountain Lion installer for on their support pages for older systems. mac os x mountain lion iso
hdiutil convert /path/to/InstallESD.dmg -format UDTO -o /path/to/MountainLion.cdr mv /path/to/MountainLion.cdr /path/to/MountainLion.iso Many websites offer pre-made "OS X Mountain Lion ISO" files