Warner Brothers' Sound Effects?

Can't help you with the device, but I jumped in here to comment on the sloppiness of the staging of some of the fight scenes.

We've been watching Maverick season 2 recently and have had to pause and back up a few times to confirm what we saw at regular speed--glaring missed punches that nevertheless resulted in the receiver falling backward like he was truly hit and the punching sound you described. I saw one last night where you could see at regular speed that Bret's fist missed the guy by almost a whole foot.

The better directors and actors/stuntmen not only knew how to make it look more like the person was really by swinging much closer to the person, but by getting the proper camera angles so as to mask any clear view, even in slow motion, that the punch actually missed it's supposed target. Here, they must have been rushing to complete their shooting and didn't bother.

I've watched some videos of what's called "Foley" work, where they dub just about all the sounds for (especially) outdoor scenes. They've been doing this ever since the early "talkie" days, so most of it's pretty low-tech. For example, when someone is walking on a gravel path, there's a box of gravel where the Foley artists walk in place, matching the timing of the actor's footsteps. Hoofbeats are made by the artists moving something like a pair of coconut half-shells, one in each hand.

This work has led to some peculiar traditions in filmed work. A bunch of us were watching an early talkie Western, and when someone fired a gun it just went "crack" and we all started to giggle -- till someone pointed out that that's what a gun actually sounds like outdoors. They were absolutely right, but we were used to more of a "blam" in movies and TV. Apparently someone way back decided that filmed guns should have a more impressive sound, so they started firing guns into rain barrels or something. And now they can't stop, because everyone would giggle.

You can find a bunch of videos showing this sort of thing by typing "Foley sound effects" into YouTube's search box. Your conjectured "punch machine" is actually a collection of pretty low-tech effects (link below). Based on your observations, though, each studio back then had its own favorite techniques.

https://www.youtube.com/watch?v=ZMlt-6XUW-U

I think it's made by a "slapstick". Two flat pieces of wood joined by a flexible tag at one end. That's where the term "Slapstick comedy" came from.

I'd say they used it a lot in Three Stooges films, when Moe slapped Curley, etc..