That's right, there have actually been a few attempts to get a 3rd Halloween Harry game made over the years. Sadly, none of them were ever completed, but thanks to Steve Stamatiadis (Via an e-mail he sent me in 2002) and John Passfield (Via his blog, 2007) some info, artwork and even a few screens have cropped up. Here you can find an overview of the attempted games.

Zombie Wars: MIA

Lunchbreak Commandoes

Halloween Harry: Undead

Halloween Harry 3

Halloween Harry: Sidewinder

Project: Xerbius

NOTE: The full text of the e-mail Steve sent to me about these games can be read HERE. If you check the links section, you'll be able to find a link to John Passfield's blog. Search for Halloween Harry to read his entries about the 1st game, as well as about Zombie Wars: MIA and Lunchbreak Commandoes.