There are some common Air Boss frequencies:
123.100
123.300
123.400
123.450
123.475
123.550
126.400
128.700
129.150
132.325
The air show organizers/air boss will pick one of these that is not used for something else in the area and that will be the frequency that the air boss uses to control the show box. It's not a bad idea to have all of them programmed, since one or more of the acts may use one of these as their "discreet" frequency.
376.050 and 384.550 may be used by military demo teams.
If the A-10 and a P-51 do a "Heritage Flight", they may use 136.575, 136.675, or 122.475.
Several of these have been used over the years at the Battle Creek air show, so they could be active for Muskegon, as well.
I encourage you to post here what you find.
Good luck, and enjoy the show!