Hi,
Here is how you could do that:
Set a really big weight for the frozen goods. That way, the australia post plugin won't be able to ship these products.
Then, create two manual shipping methods with a zone restriction to australia and a post code range restriction (one range for brisbane and one for gold coast) and a minimum weight quite big (but lower than your frozen products). If you have more than two ranges of post codes, you'll of course have to create more than two manual shipping methods...