As indicated in various Updates and Briefings, for legal instrument that enacts the decisions of the National Cabinet in response to COVID-19 is a declaration / order / direction under the relevant State or Territory public health legislation.
The are not always easy to locate and they do vary between jurisdictions. Details of the most recent declarations, with “lockdown” declarations highlighted, are included below
Queensland: Home Confinement Direction
New South Wales: all orders summarised here. Public Health (COVID-19 Restrictions on Gathering and Movement) Order 2020.
Australian Capital Territory: all declarations here.
Tasmania: declarations here.
South Australia: emergency management declarations here.
Western Australia: all declarations here.