First day of issue: 9 APR 1979, stamps designed by Max Robinson.

20c Flinders Ranges National Park SA

20c Girraween National Park QLD

20c Mount Field National Park TAS

20c Nambung National Park WA

20c Port Campbell National Park VIC

20c Royal National Park NSW

20c Uluru National Park NT

These are sometimes available on eBay. I might have a few spares if you are looking to complete your set.

Does anyone know, is there a cover with the full set of 7 on it (or even one with just the strip of 5) ?