I live in upstate NY. We got pounded a few weeks ago, and although the car did pretty good ('97 catera), it SUCKS going uphill with alot of snow, it will make it, just slowly. I have fishtailed it a couple times, and the TC kicks in and stops it dead. But snows do seem like a good idea. My spare is on a steel wheel, so someone has to make a compatible steel rim.
I am not sure if this is what you are looking for but....
http://www.wheelx.com/cadillac-cater...08036U45R.html
Other than that, best bet might be Ebay maybe?