No, Tower is not the exclusive distributor. There are a few other places where you can get those items. Many LHS can get both of them easily, sometimes for less then tower, especially if you know the management and they sell it at cost.

Also, Advantage Hobby (advantagehobby.com) sells both Futaba and OS and they have good prices. They also offer free shipping on almost everything (except oversized stuff). They are new to the scene and I have bought several things from them and their service and support is good. They even offer price matching, but I would recommend contacting them about specific items first since the WILL NOT price match if it puts them under their cost.

Hope that helps.