If you synced the iPad before you lost the notes, and not since you lost the notes, there is a chance.
Without the iPad connected, go to iTunes on your computer, open preferences and go to the Devices tab. Check the date of the backup for your iPad. If it is from before you notes were lost you can try to restore from a backup.
If not, or if it was a long long time ago so that your notes won't be there, don't bother with the rest of the post.
Disclaimer: I'm giving you the best info I've got, but things can go wrong. If you have any other choice to recover these notes, or if they are not important enough to risk your other content, don't do this.
First, while you are still in iTunes Preferences, the Devices tab, turn off auto-syncing. This will keep you from accidentally overwriting the backup file when you connect the iPad.
Second, consider the content in every other app you have. With the exception of the music, books, apps, tv episodes, and other media that are stored and viewable in iTunes on the computer, it's going to be overwritten by what was on the iPad at the time of the backup.
If you do not have your contacts or calendar info synced somewhere else, they they are going to get reverted to what they were at the time of the backup.
Email, or otherwise transfer this stuff to a safe place where you can load it again later.
Now connect the iPad to iTunes.
Right click on the iPad under the devices list to the left and choose Transfer Purchases. This probably isn't necessary, but it might save losing media you loaded on the iPad, but haven't synced with iTunes yet.
When that is done, right click on the iPad again and choose Restore from Backup. When it is over go to the Notes app and see if you got them back.
As I said, this is a last ditch chance to get the notes back. Other options are preferable.
Whether you get your notes back or not, I recommend looking into Evernote. It stores your notes online and syncs them with just about any device or computer. The organization and search tools are much better than the native app as well.
If you get your notes back, Evernote comes with an email address. You can use the send email option in the notes app to send your current notes to Evernote, making the transition a bit easier.
