Found it. I know that these were at least used with CA50. The EOL part number is 50-11300-173. I need 15 for pilot.

And what about above mentioned 21-69024-01R?

The only wired headset solution that I found for the MC7xx family are the following:

1) RCH51 - Rugged Cabled Headset and also Headset Adapter Cable (25-124387-01R)

2) 21-69024-01R - Used to make phone calls

Well, try it on a Milestone phone and see if it works! Or any other Motorola phone....

I need a wired headset solution for MC75A, and the headset in the picture works, but I don't know where I can purchase.  Don't know the part number.

looks very similar to the one for SB1 or MC40
21-SB1X-HDSET-10R (10-pack) (never seen one but per specs it should have mike and volume control)

21-154925-01R is a PTT headset, "Push-to-talk (PTT) corded headset, mono with microphone for ET1 Enterprise Tablet". Yet, I can't see any sort of PTT button on the picture. However, I do not have any to compare with. To me, it looks more like a version of 21-69024-01R. Anyway, I suspect this model rather belongs to former Motorola Mobility, to be used with smartphones. This big logo on the very speaker makes me think so.

First, thanks for your responses. It's not  21-154925-01R.  It doesn't have a button, just a clipon mic.  I've tested MC75A with 21-154925-01R, and it doesn't work. Regarding it belonging to Motorola Mobility, maybe, but the earpiece resembles some of our other earpieces.

From your pic, it looks like it is Part Number 21-154925-01R.