Correlate Geographic data

I’d like to generate data from country down to postcode level but noticed that the post code is not related to the states and maybe even the lat & long.
What is s the best way to achieve this?

“country”:“Australia”,“state”:“New South Wales”,“latitude”:-33.7974423,“longitude”:151.2502275,“postalcode”:“1161”}

Observation Postal Code 1161 is not a postcode found in Australia.