Well such a list might be hard to publicly come by since Mobilcomm does the programming for Clermont County agencies so unless you know of someone who works for Mobilcomm who could get you a list it might just come down to you having to listening and doing it yourself.
Your right it doesn't hurt to ask. But I'm saying you won't find an Official list online unless someone from the inside puts it online and I doubt that would happen. Under MARCS agencies based in a specific County there ID will start with the County number followed by a two digit agency number followed by three digits which would be the radios individual number.
I think your bigger problem will be, other than knowing that a radio exists, you won't know who has that radio, other than a general department.
Very few people in a fire department have an assigned radio. Out of our 60+ members, only 6 have radios assigned. Out of the radios we have, mobiles are mounted in trucks & vehicles, but portables change hands every morning.
Which will only come with the mobile IDs. It will require a lot of listening.
The system only sees IDs, not specific radios. Furthermore, you may be able to narrow a radio to an agency, but not further. A radio can change Who IDs with it daily, especially for police, when officers are in different cars and on or off duty.
Fire Departments keep things more static, but those do change when vehicles come out of service for maintenance.