I really can't think of anything that meets your criteria.
For something to have been introduced to the U.S., it would mean that food item would have had to have originated in Australia. And about the only thing that I can think of is Vegemite, already mentioned.
There are some recipes that are Australian, such as Pavlova. It isn't very popular over in the U.S. and most people have never heard of it - but a pastry chef would probably know about it and has made it sometime during training.
I think the only way we can get Kangaroo meat over here is to mail order it frozen from Oz...and I'm not sure how legal that is. (meats have to meet certain requirements in order to cross borders)