This app was mentioned in 2 comments, with an average of 7.50 upvotes
Android link for anyone interested: https://play.google.com/store/apps/details?id=au.gov.rba.rbabanknotes
Guaranteed fresh ones - go to head office of RBA at 65 Martin Place.
Australia Post will also sell you a $5 note in a special folder for $11
Learn about the new security features here, or download the 'RBA Banknotes' app (android, ios)