Having done a lot of large event rentals in a previous role, often the "event" is on the temporary radio system with all of the security, vendors, medical, maintenance, electricians, etc. Fair grounds typically have very limited radio systems with just a few channels like OPS, Security, and Maint.
A large event may need dozens of channels to cover all of the people using radios. In the past, I have seen both the facility hosting the event abandon their radios for the duration of the event so everyone is on the same system AND have also seen a representative monitoring the temporary radio system and relay to Maint/Security/Medical/ETC on their normal channels.
Bearcom reall like single site MOTOTRBO Capacity Plus systems in UHF. They have an extensive rental department with a lot of resources. My gues is a 4-5 repeater Capacity Plus system with a few of hundred radios.
TT