Horizon Hobby brand product resellers - Just pick your state and hit Search. (most hobby stores)

Thunder Tiger also has a list of stores throughout the US that carry their products. Again, not every store but most of them! This link goes to a search on the mfg website.

Kyosho also has a list of stores throughout the US that carry their products.

Miniature Aircraft's list of stores.

Great Plane's list of stores.

Great Planes Distributors sells many brand names in RC. Go to their page, pick the product mfg you're looking for and then search "where to buy."