Does your air show have a dedicated radio frequency for the event? Do you have a secondary and discrete frequency? Why not?
According to the FAA guidance on aviation events, to receive specific frequencies and authorization to use them, event organizers should put the request for frequencies in the remarks section of the FAA Form 7711-2, Certificate of Waiver or Authorization Application. Your local FSDO will initiate the coordination with the regional Airspace and Rules manager, Office of System Operation and Safety (ATO-R).
Don’t expect to do this at the last minute. Plan at least 90 days to work through the coordination.
Don’t jeopardize the safety of your event by not having workable frequencies to keep the airways free from chatter. The system is there. Use it.