Are there any civil defence guidelines for what to do if Australia was attacked by another country?

Yes, there are civil defence guidelines in Australia for responding to an attack by another country. The department of Home Affairs, which heads the Civil Defence branch of the ADF, publishes general preparedness guidance on their website at the following page and is the leading authority on this kind of preparedness:

https://www.homeaffairs.gov.au/prepare/natural-disasters

https://www.homeaffairs.gov.au/prepare/emergencies

The Home Affairs department has an app "Get Prepared" which can also provide further assistance.