Update: Different dealer in the area had a left side steering wheel switch in stock - "one of 31 dealers" in the country with that item, so I got lucky. That dealer performed the repair. I wasn't in the shop, of course, but the tech brought stuff out for a show&tell. Here's the nub of what he told me:
1. A modified diagnostic procedure is fairly new from the manufacturer - as in late last year. The switches are back-ordered due to unexpected demand but the manufacturer is beginning to catch up.
2. Apparently the switch does have programming circuits; other dealers were mistaken. That's what "breaks", not mechanical parts. A power-out/reset will often restore the switch circuit programming, but it's almost always in failure mode and will "break" again due to repeat circumstances that creates the initial fault.
3. The SCCM throws codes that are not accessible through OBD2, and the tech told me that those codes only happen in specific conditions. That portion of the diagnostic is both broad (applies to multiple systems) and robust and rarely fails to indicate problems accurately. In my case there were no SCCM related codes, so the conclusion was that the problem lay "above" the SCCM - in other words, in the switch or related wiring.
4. Clockspring problems occur. However, when they do, they do not affect the left-side switch alone; they almost always affect other controls as well.
Again, this is what I was told, and time will tell.