Amazon only keeps backup notes for stuff you've purchased from them.
If you need a text copy of your notes and feel comfortable installing/using Perl, you can try the free
MBP reader script which someone has reverse engineered from the .mbp format.
If your notes are mostly highlights, you should also be able to find their full text in the MyClippings.txt file on the Kindle itself, which you can copy over and edit on your favourite word processor.