I need it too, Ive been waiting for it since I finished this series the first time. Its just not fair. Devilman Crybaby finished alredy. We want this thing back now.
It's a shame we never had Shin Great Mazinger, but you can play it with an "alternative" version of what could have hapened at the end of the series in one of the "Super Robot Taisen" games. It has a playable Shin Great Mazinger