Hi, Australia does not have a single BMD but instead each State has their own records. Some are free to view on line others are pay. But, and this is a biggy, we have stringent privacy laws and in the case of births no information is available on possible living individuals, IE a 100 year rule is applied that is births are at present only available prior to 1911.
In the case of Marriages it is 1961 and Deaths 1981. The Laws of the Commonwealth of Australia were set up in 1901 at Federation and allowed for the States to maintain their own Judicial system under individual Governors.
I know, it makes it tough to check records for us family Historians but thems the breaks. We have in some cases been lucky as births may have been published in Newspapers and we can check these up to 1954 I think, via TROVE. This is our national online database of Historical Newspapers.
Hope this helps
Neil