The issue with MP-05 is that it is classified a replica firearm (despite it's massive oversize). Owning firearms and replica firearms is illegal without a permit and safety measures put in place for its safe storage. In NSW permits are only granted where one has a legitmate membership in a gun club or sporting group. Consequently Tilby set up the Megatron Ownership Club (or something like that) and has to store Megatron in a sealed case within a locked room.
It's not about circumventing the law, but about the measures one needs to put in place to legally own a replica firearm figure like MP-05. (And probably the legion of 3rd Party Megatrons that have recently been proposed.)