The working part of any kazoo is just a small piece of paper/film stretched over a hole. You can alter the shape of the area which projects the sound...(as in the 'trumpet' linked to above), but most of the sound, as leenia suggests, IS produced by YOU. I have an old one with a bell at the end and an added Sousaphone type bell over the sound hole that I can actually rotate to function as a monitor...or even cup my hand over like a mute. But *I* still have to produce the basic sound by humming.

I have a fancy wooden one with two sides, but it it mostly for looks, and still has only the basic paper to vibrate.