Clean reinstall of Mountain Lion deleted my iLife applications. How do I get them back?
This depends on whether your copy of iLife was purchased through the App Store, installed from DVD, or was just the version that came with the MacBook originally. If you had purchased from the App Store, it should be just as easy as going to the app store and redownloading your apps. If not, then you'll either need to reinstall from DVD or purchase the new versions of iLife. Your MacBook should have come with an install DVD for both OS X, and for iLife.

Another solution is to use the Migration Assistant and Time Machine to restore your apps. That's by far the easiest way to get all of your old stuff on your new system. Of course, it'll pull in more than just iLife.

Finally, if you have a Time Machine backup, you can still restore from it. Option-Click on the Time Machine icon at the top right, and choose "Browse Other Backup Disks". That will let you get into the backup from your previous setup.

Good luck!