This one by North American Arms has a derringer type grip and trigger but it's a 5 shot revolver in 22 Mag. You can get it with an extra 22LR cyl, too, just like a real Ruger Single 6. They say it's carried with the hammer down between 2 chambers so it can't fire in your pocket.
I suspect that you don't have to hit him with the bullet. The muzzle blast should put him down.