Not too sure what you are after. I presume you are referring to the diaphragm of a Claxon type horn which have an electric motor that spins with a small star wheel attached to the spindle. The raised serrations on the face of the star wheel rub against a metal tooth protruding from the centre boss of the diaphragm which is made from thin (approx .020") very springy steel. The tone of the horn is adjusted by increasing or decreasing the pressure with which the two parts meet. (adjusting screw on back of horn and slightly moves the motor armature forward or back).
Swap meets are usually scattered with incomplete horns of all breeds, and it is just a matter of getting one that will fit/adapt to your situation. I have found not too heavily rusted (pitted) diaphragms work OK when cleaned up, but do not paint it as this acts like a dampener. Not sure what the best protective coating would be, maybe a very light coat of etch primer (clear watery type). The diaphragm is fitted each side with a thin paper gasket approx 1/2" wide,where it clamps between the horn funnel and motor housing.
Earlier '25 Superiors had an inferior Remy vibrator type horn protruding through a hole in the firewall, and make quite a different sound, more like a frog burping, and feeble at that!
Sorry I can't oblige with photos. All too much stuffing around for my intellect to fathom.