Hello, looking through a stamp magazine I came across an article on the first England-Australia special airmail stamp.
I found this copy listed on eBay. really nice I think you will agree.

On January 15th 1920 steps were taken to issue the airmail stamp following advice from Ross Smith about the number of letters being carried by air. The design features a Vickers Vimy. The inscription reads First Aerial Mail England-Australia 12 Nov – 10 Dec 1919. The stamp was printed by lithography in deep blue from a copper halftone block. The full story of the stamp would take a lot of writing but an excellent write up exists in the July issue of Gibbons Stamp Monthly. Tthis is a stamp that was not a stamp but instead a commemorative label for use on an historic airmail. And it is valuable. The Australian Air Mail catalogue lists this from $20,000 mint and $9000 on cover, or you can get a facsimile on eBay for 5 bucks!!!