If you backup with iTunes and you restored from the backup and the notes were gone, then there is no where to retrieve them from unless you have another backup that contains those notes.
Launch iTunes on the computer and go to iTunes>Preferences>Devices. You will see a window with all of your backups listed in it.
If you see a recent backup that you are certain contains the notes that you need, recover deleted notes from that backup.
I think the suggestions might be of use to you.
There are a few good ways to go. I would try them before help others. Check out this guide
In my experience the methods in the guide have been as good and many times. Hope it can help you too.