You can make one yourself.

Or, if you want to buy them (as I do, I'm lazy), you can get them from FlyingZ hobbies or a guy who goes by the handle "proppy john" on the rcca forums at www.rccombat.com. Just go in to the forums and do a quick search, you'll find him pretty easily.

flyingZ's phone is 270-835-9001. They have a website, but I haven't been there in a while, dunno if it has online ordering or not.