Oh. I just realized that you don't want the AB-2D, which can be found, you want something like the AB-2D but with three switches. An AB-3D if it existed.

If I were you, I'd go rotary. Check a surplus place like All Electronics in Van Nuys, CA, or Apex Electronics in Sun Valley, CA (where the actual parts used to make the original Flux Capacitor were purchased) to see if they have any rotary switches. You'll need 4 poles, 3 positions (4 positions if you want an OFF position, 5 positions if you want it to go A, off, B, off, C), some solder, and a nice knob.

If the switch is make before break, you definitely want a 5 position switch. If it's break before make, 3 position is okay. Ask me how I know.

And tell the client never to switch with the volume at MAX.

Edit:
You can, with the help of a salesperson, get the parts to construct this switch. See [Link: alliedelec.com]. That's your basic building block.

You get four of the switch wafer Electroswitch Inc. D2D-51, shown at that site, plus parts to assemble them onto a shaft and parts to limit the rotation to however many positions you need. I first built some of these in 1966 and, oddly, most recently threw out a half dozen of this type of switch about six months ago. Too bad.

It's a rotary wafer that comes able to switch anywhere from two to twelve positions. You get four of these and the hardware to assemble them to look more or less like this:


Except the one in the picture has only three poles.

Anyway, there are parts to space the wafers apart and parts that block the rotation of the shaft. That's how you make it go fewer than 12 positions.