Assuming you are dealing with a US supplier that requires it, just let them know that you are not a US resident. Most won't need you to complete that part and if they still do insist because it's a required field that needs completed to process, then you can use your own tax id. In Australia, ABN is fine, but very doubtful they will request it.
That's for domestic US customers, not international customers who pay tax elsewhere.
Cheers