Some areas of the U.S. and especially Canada are experiencing a short supply of winter tires. The cause has been linked to an increase in demand in Quebec due to a new law. If you are having trouble getting snow tires for your vehicle, this may be very well the reason.
http://www.cbc.ca/canada/ottawa/story/2008/11/14/mtl-snowtire-cp-1114.html
http://www.cbc.ca/consumer/story/2008/11/20/nwt-tires.html