Welcome to the forum. You could take a feed from the output side of your existing horn relay to one of these:
htp://wwww.ebay.co/itm/VINTAGE-CASEY-JONES-TWO-WAY-BYPASS-LOW-RADAR-REFLECTION-AIR-CONTROL-VALVE-NOS-BOXED-ORIGINAL-CONDITION/360747974711?pt=LO_Def
If it's stealth, keep it under your hat.
