Air horns can be had in many places depending on quality. I think walmart even carries them. And rejetting is done by replacing the two main jets in the carbs with different size main jets. If you haven't had your carb bowls off recently then you will have to take the carbs off to do it. Otherwise a 2 inch #2 phillips bit and pliers or a bit on a 1/4 drive swivel will help remove the screws holding the bowls on.