Usually we don't carry them because they eat our fish. Occasionally, a pet care department manager will be kind enough to order them for a customer, but usually not. Big stores in cities, like NYC, will carry them because they have enough space for species only tanks with them.
I get mine from crayfishing, ebay, aquabid, online stores, LFS, etc. You can find a lot on the net if you want to have them shipped, but you're in a great state for fishing out a whole bunch of different species from your streams, rivers and lakes.