There's a link off wikipedia that directs you to an online retro arcade where you can play it, I think.
Zoombie, which stage did you think was harder--Barricade Zone or Bellon? Personally, I think it's the latter. Barricade Zone is much easier once you figure out when to go where but Bellon is just...so many missile on the screen at once. =P
And homing shots are overpowered.