There is a Paradroid project at sourceforge
http://paradroid.sourceforge.net/
And MobyGames has some information on the Amiga version.
http://www.mobygames.com/game/sheet/p,24/gameId,9488/
Lastly, HoTU has a fan-remake for download.
http://www.the-underdogs.org/game.php?id=4055
Enjoy!
