Australia New Zealand Food Standards Code Labelling of irradiated foods
I finally had a response to my email asking about labelling, but have yet to find such a label on foods. There were a number of urls though:

"(1) The label on a package of food which has been processed by ionising radiation must include a statement that the food has been treated with ionising radiation.
Examples:
‘TREATED WITH IONISING RADIATION’
‘TREATED WITH IONISING ELECTRONS’
‘IRRADIATED (name of food)’

(2) The label on a package of food containing an irradiated food as an ingredient or component, must include a statement that the ingredient or component has been treated with ionising radiation, either as part of the declaration of that ingredient or component in an ingredient list or elsewhere on the label.

(3) Where an irradiated food, or a food containing an irradiated food as an ingredient or component, is not required to bear a label pursuant to clause 2 of Standard 1.2.1, there must be displayed on or in connection with the display of the food a statement that the food has been treated with ionising radiation, or that it contains an ingredient or component that has been treated with ionising radiation, as the case may be.

(4) Notwithstanding clause 3 of Standard 1.2.1, the label on a package of irradiated food which is sold other than for retail sale must include -
(a) a statement that the food has been irradiated; and
(b) the minimum and maximum dose of the irradiation; and
(c) the identity of the facility where the food was irradiated; and
(d) the date or dates of irradiation."