Oh, you won't find it easily. Irradiation has yet to catch on in the US. It's very common in other countries and the quality of irradiated produce, especially tropical stuff that can't be grown here, is usually pretty high - but American consumers just won't accept it yet. It's a shame, because it's so promising and could prevent so much waste. The symbol is called the Radura, btw
(I'm the captain of our school's college bowl team, my brain is filled with trivia)