I haven't heard of a "fly anywhere" code for Platinum regardless of game version, even though US and JAP map location code are slightly the same, there isn't proof that the fly anywhere code worked in D/P. Personally, i find the fly anywhere code insignificant because cities are scattered around Sinnoh making it easier to reach other specific locations. The move anywhere code is quite useful already so i think asking for a fly anywhere code would be pushing it.