I also don't have problem finding sours, and they aren't more than any other craft beers. I find Belgian sours tend towards pricey 750's, while American and Berliners tend to be average price in 6 packs. In the midwest a store with a decent stock should at least have Bell's Oarsman, which is a great just-drinking-some-brews beer.
Boulevard makes a few sours that are pretty easy to find as well. You probably don't even realize you're walking by sours, since they don't usually come out and say SOUR BEER HERE.