How to recover missing notes since Mavericks update?
The notes should be stored in your backup, at least. Check here

Solution is to navigate to ~/Library/Containers/com.apple.Notes/Data/Library/Notes and restore:

NotesV1.storedata
NotesV1.storedata-shm
NotesV1.storedata-wal  

Where ~ is your home directory e.g. /Users/your_username

Refer macrumors
or apple discussions
for more info.