Seriously Griff, you need to make a sticky for this topic somewhere mate. About 3 times a year this topic with the same queries comes up.
Seriously - has ANYONE in Aus actually gotten charged for owning an MP Megatron? And if so was it even remotely recent? I really don't think with all the heavy stuff going down in our communities than anyone except the most pedantic of cops would care. And I bet no one is checking houses for them. All my neighbours own REAL guns - the coppers round here couldn't give two shits that I own a little toy robot that turns into a fake firearm and I would get openly laughed at if I brought it to their attention.
My advice, just don't worry about it. Unless you make a massive deal of it I don't think anyone in authority gives a crap - they have bigger fish to fry.