Backed up and restored to my new air. Saw my books in I books then lost them. Help

How did you backup and restore, and did you do File > Devices > Transfer Purchases before restoring ? A backup on a computer's iTunes doesn't contain your iTunes downloads, the restore will pick them up from your iTunes library - so if you didn't have your ibooks in the Books part of your computer's iTunes library then the restore won't be able to put them back on your iPad.

If they are still in your country's store then you should be able to redownload your ibooks via the Purchased tab in the ibookstore in the app. You can then copy them to your computer's iTunes via File > Devices > Transfer Purchases so that they are on there if you need to restore again.