That's hard to predict. Rodimus was plentiful, but Optimus Prime was hell rare, but then much later popped up in quantities in a few locations. <shrug>
Nice!
I'd say about a year (give or take a month or so). MP10 was released in September 2011, and the Hasbro version came out here in October 2012 - so it was about 13 months between the Japanese and Australian releases. That's not too bad. (it's just finding the sucker that was the uber frustrating part)