I was looking at the locking one from finishline as well. I can't see why this would not be ok in Australia with a sticker on the top saying unleaded fuel only. A bit of a silly requirment now, leaded fuel is not available anyway.
The only other thing I can think of is the anti syphon flap and the nozzle diameter. The old leaded fuel nozzles were a bigger diameter so they would not fit in an unleaded filler.
I was just going to use a poor quality sticker that peels off easy.
http://www.finishlineaccessories.com...roducts_id=383