The first VWs sold in Australia were imported by Spencer Motors in Melbourne. Lionel Spencer imported two Beetles in October 1953 and they were sold through his Melbourne dealership. He used to be a DKW dealer before that. Local assembly of German CKD kits began in JUne 1954.
No one knows if those first official cars still exist.
There are plenty of earlier VWs here, but all have been privately imported, either by individuals or by the military. The army did bring in two VW Beetles for evaluation in 1945 but both cars were run into the ground. Graham Lees owns the remains of one of them, which as Guy said had been rotting in a field in Tasmania.
In 1961 VW Australia celebrated their 100,000th Australian sale by looking for the oldest running VW in Australia. They mounted a huge campaign in the media and advertised widely for owners of old VWs to come forward. Eventually they found a German couple called Mr and Mrs Haenel in country Victoria, who owned a 1946 Beetle that they had brought with them when they migrated from Germany in 1951. VW Australia swapped them their 1946 Beetle for the brand new 100,000th Beetle. It was quite a ceremony, hosted by the then Victorian Premier, Sir Henry Bolte.
VW Australia displayed the 1946 car for a number of years, and it could be seen at their Clayton headquarters. It was sold at some stage, probably when the plant was sold to Nissan, and it ended up at Gilltrap's Car Museum at the Gold Coast in Queensland. When that museum went out of business in the early 1980s, it was bought by the car museum in York, WA, where it was on display until recently. They have just expanded to a new facility in Fremantle in the last few months, and last I heard the 1946 car has been moved there. It's in beautiful condition, in blue-grey paint. I saw it in York myself in 1987. The museum's webpage is
http://www.yorkwa.com.au/Motor.Museum/index.htm
But unfortunately doesn't feature the VW.
Since then several private collectors have imported World War 2 Kubels and Schwimmwagens and other old VWs too. Impossible to say now which one is the oldest, but the one owned by the War Memorial in Canberra is indeed a veteran of the North African campaign in 1941, rather than the European or Russian fronts of 1944 and 1945.