Car stereo

I'm not sure where this would be posted so some help please. I just thought I'd start here since it will be for an event..
So I've been approached with a question and i'm not sure how to answer it. My buddy organizes and runs an even every year for the offroad community. The racers all have race radios(VHF mobiles) to get information on when to start their runs and what ever else.. The crowd does not know what is going on unless they have a scanner or VHF radio as well. The place is way to loud and big for speakers.
He asked how(if its possible) we could set something up so spectators in their vehicles at the event could tune to a certain station on their car stereos and hear up dates from the organizers during the event..
Is this possible or way out of our reach? We still have a full year to plan and set up in need be.

Thank you!

There are the transmitters used to transmit Drive-In movie audio to the attendees' vehicles at Drive-Ins.

http://www.jackroeusa.com/Stereo-drive-in-transmitter.html

There are also those transmitters used to advise motorists such as entering airports, highway construction, detours, etc. You have probably seen them along the road, "For Information tune to 1600 AM on your radio".

http://www.amsig.com/HAR/

Hopefully you can find a supplier that may be willing to rent one of these units.

got it thank you for the help