For a Ringmaster they need to be between 3/4" and 1 1'4" tall, depending on how the bell crank is set up. Most well stocked hardware stores sell hard aluminum angle that is 1'/16" thick and I've made horns from that before. they may even have T stock also and that may be better. All you need is a drill and a hacksaw and a few minutes work you have a control horn.
Type at you later,
Dan McEntee