Freddie here from the Shopify Support team, happy to help!
I've found a few apps from our Apps store that look to have this feature you're looking for!
Otherwise, you can look into hiring a Shopify Expert to build you a custom solution.
Let me know if this helps!
Shopify Support - email@example.com
It looks like the Australia Post app just pulls and calculates rates from Australia Post. I don't see anything that integrates directly with Austlira Post, but check out StarShipIt, which can sell you the postage and looks like a more complete solution. Perhaps that will be helpful. I am not the app developer, and I haven't tried this app.
Hello @Shane_Major ,
You can check out the Australia Post Rates & Labels app. The app helps you integrate your Shopify store with the Australia Post account.
You can display real time Australia Post rates at checkout, generate and print Australia Post labels in bulk and also handle Australia Post tracking.