Good question. Of course, the answer depends upon when the Buccaneer enters US service. How about 'A-11'?
There's no confirmed A-11 designation in the current system (A-10 was applied in the '70s, A-12 in the late '80s). Going by the F-111C and F/A-18s, I doubt that Australia would apply its own designation. Maybe JA-11 for the JASDF?