Actually, there are a few. For example, QLD 4352. It's just a collective postcode that covers everything around Toowoomba that hasn't been given a postcode. Using the suburb name instead of 4352 is a whole lot more productive.
It's eight non-contiguous areas as far north as Caboolture and as far south as Casino, the biggest of which are not much larger than Brisbane City Council.
Edit:
There's a treasure trove in the post code boundaries of utterly bizarre things that only past houses being in weird places can at times explain.
