Staring at the lettering on the side revealed that it was a Cherry brand switch, and in fact that it was from the WR series. From there it was just a matter of decoding the option codes: circuitry, actuator, marking, housing color, function, etc. And that gave me the exact part number:WRG32F2FBBN.
Plug that into Google, and you get links to distributors, like Allied and Mouser, offering the part quantity one for $1.16 and $1.34. Looks like Miller paid about $0.75 for them in quantity. Oh well. I could have saved a few bucks, except the shipping would have probably wiped any savings out.
Well, if I ever build my own welder, I'll use a switch just like Miller, and I know where to get them.