There are many sources of R/C equipment. The first source should be your local hobby shop. In Waterloo, that's HobbyTown at 2204 Kimball Ave, Waterloo, IA 50702. They carry electric powered aircraft, drones, Spektrum transmitters & receivers, 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 the following list.
Online Stores in alphabetic order
Note: When ordering from Bang-good or HobbyKing, you can specify warehouse location. If you order from Hong Kong, your order can take anywhere from one week to several weeks due to shipping times and US Customs clearance. Ordering from a US warehouse has normal shipping times of one week or less.
Radio Control Sources: (Partial List - More to Come!)