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.
Thanks a million! this actually just helped me to recover all of my usernames and passwords that I had jotted down over time in my "notes" (my only copy). On 2 separate occasions, this information mysteriously disappeared off of my iPhone (I'm wondering if any others have had notes disappear, also?) The last time was over a month ago and I had come to terms with the fact that all of that info was long gone. Today, I opened up my "notes" on my iPad & there they were! Without much thought, I brought up a different doc and tried to go back into my newly found one. It was gone once again. But, I thought there has to be a way to retrieve it because it was just up on my screen 30 sec.ago. I came to this site and every thing that I read about the subject said I was SOL unless i had previously ran a back up (which i hadn't). So, thanks once again and I hope anyone else unfortunate enough to have this problem will not be discouraged by all of the wrong info out there.