There are many sources of R/C equipment from ARFs to Warbirds. The first source should be your local hobby shop. In Waterloo, that's HobbyTown at 2204 Kimball Ave, Waterloo, IA 50702. They carry Horizon Hobby products including Eflite, HobbyZone, Hanger 9, Blade and Spektrum plus Ares drones, batteries, fuel, adhesives and building supplies. If they don't have it in the store, they can order it for you with delivery in a couple of days.
There are some things that cannot be found or have a limited selection at your local hobby store. For those items, you need to go to the Internet. The problem is you can't tell good vendors from bad ones. To help you find those unusual things from good suppliers, we've compiled a list under the "Sources" tab to help you.