Interesting story on the internet about which cars are the hardest to get a hold of and the showroom supply:

Turns out the Dodge Charger made the list with an average of a 24 day supply
(Maybe the Charger is taking sales away from the Challenger, or perhaps people want/need the extra doors)
Below is how they calculated the numbers:

"To compile our list of hard-to-get cars, we used inventory data from Wards Auto, an automotive data and analysis firm based near Detroit. We calculated average day-supply rates of 2010 model-year vehicles for March, April and May to figure out, on average, just how quickly these cars leave the lot. (Day-supply rates are inventory numbers, divided by the daily selling rate that month.) Then we spoke with manufacturers to get a street-level sense of how long cars typically wait for buyers, since day supply data can fluctuate from month to month."