I doubt anything like that has ever been made, as the 120 preceeds the "tacti-kool" era. If you really, really need one (and I assure you that you don't) buy an extra part, take it to a welder and have it welded up, file away everything that doesn't look like an oversized control, and cold blue it.
Proper technique will get you where youre trying to go. Empty the gun. Double check that it's empty, both chamber and magazine. Dry fire it in a safe direction, and stop. You now have a gun with an empty chamber and the hammer down on the empty chamber. At this point you don't have to hit the slide release to cycle the gun. If you load the tube, the gun is now in what's called "cruiser-ready". Empty chamber, hammer down, mag loaded. To bring it into action all you have to do is cycle the gun.