The only carrier we are integrated with for their real-time rates are:
USPS
UPS
FedEx
Canada Post
DHL Worldwide
We don't have integrations for AU Post, Royal Mail, or any other carriers. This means that you would instead have to use rule based rates, like 'By Weight', 'By Price', or 'By Items' to configure your rates, the rates won't be directly from the carrier, but you can try to come up with a rule based rate to best match what the rates would be.