(Sample data) Australian Postcodes in geojson format Based on Australian Bureau of Statistics data: http://www.abs.gov.au/AUSSTATS/abs@.nsf/DetailsPage/1270.0.55.003July%202011?OpenDocument
More details can also be found here: http://census.okfn.org/country/Australia/postcodes
Made with mapshaper ( https://github.com/mbloch/mapshaper ) and a little bash fu.