If you can find out what the "Air Boss" frequency is, thats where a majority of comms take place. A few weeks ago at McGuire's show, the freq 120.0 mhz was used.
I spent the afternoon today at the Millville Airport watching a free show.
Frequencies used Thursday and Friday,
284.2500
237.8000
275.3500
346.5000
135.6500 Air Boss
118.7000 Airport Ground and Aircraft parking.