Amazon.com: Pyle 100-Watt Megaphone Bullhorn, Lightweight and Portable Loud Air Horn with Aux (3.5mm) Input for MP3/Music, Automatic Siren, MIC/Talk (Black), 1500 Square Yards Projection Range : Electronics
Freesound - "SFXsource.com-Free-Airhorn-DJ-Sound-Effect.mp3" by SFXsource.com
MLG AIR HORN sound effect - YouTube
Fiamm Tour Horn or cycling horns. Also knwn as Tour de France claxon - The HornWarehouse.com A warehouse full of air horns, melody horns, bells, callhorns and other stuff that makes noise