theres lots of options. you can get one at a pet store (not the best option but still an option), find a local breeder, order one online from sites such as kingsnake.com or fauna classifieds, or find a show near you. this is a good list of shows here http://www.reptilechannel.com/reptil...le-events.aspx or you can just google shows in your area. hope it helps.
Make sure you do your homework ahead of time and have everything setup and a basic understanding of care.
From there I would go to a reptile expo because you'll be able to see what you are buying before you buy it. At a pet store they are going to charge you an arm and a leg for a normal ball python that you can get for pretty cheap directly from a breeder.