20% off on The Good Guys gift cards when purchased at Australia Post from 30 April to 13 May.
PS: Although the deal technically starts on the 30th, some Australia Post outlets seem to be honouring the deal now.
PPS: Looks like the link has been photoshopped out of the Australia Post official catalogue. And the link has been removed from Lasoo. I've updated the link to the catalogue. It is on the bottom of page 5 of the catalogue.