...I'm not quite sure how everyone feels about Retro-Bit's re-releases but they have an upcoming release of four classic Toaplan shooters for the Genesis/Mega Drive. Truxton/Tatsujin, Fire Shark, Hellfire, and Zero Wing are being offered individually as well as in a complete collection. Having had Truxton and Hellfire slip through my hands not so long I'm thinking about placing an order, I may pull the trigger on Zero Wing too.
http://retro-bit.com/toaplan-shooters/