I know, and nerd points to short-carabine for his earlier post. Same goes for a lot of the fascinating late Victorian/Edwardian pistols. If they aren't in big movies or video games, they won't get made.
The Mars is insane. Steampunk Automag that doesn't work properly. The British Army used to keep a particular WW2 prototype tank (I forget which, I think it's at Bovingdon now) to teach people how not to design tanks, because it was so awful in every respect. The Mars is the pistol equivalent of how not to do it.
What would be AWESOME would be a genuine semi-auto pellet-firing CO2 Webley-Fosbery.