Update:
I called my local guys again - got the manager this time and asked about the size discrepancy - it didn't sound right to him. First time, I just told the counter guy the car I had, but this time he asked me the tire size. He confirmed that our car should have the smaller size, and that it is indeed an unusual size - small Prius's (Pri-i?), and some Minis are about it. They can easily get Bridgestone Blizzaks (which he says he likes) in the right size or special order something much more expensive.
As for wheels, I'm still on the fence. Right now, I don't "waste" time on swapping tires, because I take the car to them - and they do the job in the time it would take me to switch wheels myself. Plus, they check and adjust the balance of each one, each time. It does cost money, of course...
Junkyards and Craigslist around here are a challenge - you have to either wait for a local deal, or be willing to drive pretty far. Plus, there's the cost of new tire pressure sensors in all 4 wheels - I wonder what the ramifications are of running without them? Dash lights on all winter, probably, at a minimum? She won't go for it.
I'll probably just get tires now, and look into new wheels for next season...