Can Australian passport holders obtain multiple entry tourist visa in HK?

Well, it is realy hard to answer this question. It is possible to get one in HK, but for the entries, it is all up to the consular officer, with the documents you provided such as itinerary or invitation letter. You can submit your application to The Commissioner's Office of the Ministry of China Foreign Affairs. Generally, the processing takes 4 working days, and express service is available. Fee for half year multiple is HK$500 and HK$800 for one year multiple.