There are some online sources, such as My Pet Chicken, or you can find local hatcheries, like Sunnyside Hatchery, in Beaver Dam, WI. You'll need to do some research to find out where to order the particular breeds you want.
No matter where you order them, they will most likely arrive via the United States Postal Service. Some mailmen will deliver them straight to your door, others will require that you pick the little fuzzballs up at the Post Office when they arrive. I always get a kick out of the carrier's face when we get deliveries at work... he's always very relieved to be bringing in that box of 100 or so chirping chickens from his hot, steamy mail truck!
I ordered most of our chickens from My Pet Chicken; they will be arriving at the end of June-all 15 of them! The only chicks I got elsewhere are my five little Silkies. They weren't available until the end of August from My Pet Chicken. I wanted them sooner, so I found a private local breeder in Mequon.
FYI...Baby chicks don't need food or water for the first 72 hours of life outside the shell because they are still ingesting their yolk sacs which provides them all the nourishment they need. Once you get them home, you need to provide them with warmth, food, water, and a safe place to stay immediately.