I'm new to the programming world, and I thought I'd start off by saying that I'm a volunteer firefighter and my department isn't that well funded. I'm trying to get the frequencies for Harrison County, specifically VFire 21, an interoperation/interagency frequency used for fireground operations.
VFire 21 is easy. Talk to the SWIC, as mentioned above. The Statewide Interoperability Coordinator should be able to give you some guidance on what should be programmed into your radios to allow interoperability throughout the state.
If you are going to get into programming other agency frequencies/systems into your radios, you need to take some additional steps:
-The FCC is exceedingly clear on the point that you can only program in frequencies you are authorized to transmit on. That authorization comes from FCC issued licenses and licensees. Programming in the national interop frequencies would be covered under FCC rules and through some statewide licenses.
Programming another agencies specific frequencies into your radios requires a memorandum of understanding between both agencies.
-Please, please, please do NOT rely on Radio Reference database as a source for programming your radios. This is a hobby oriented site and the database info is submitted by hobbyists with scanners. The frequency/tone info can be incorrect/totally wrong. The only correct place to get frequency info from is direct from the licensee. This not only assures you are getting all the accurate info you need, but also lets them know they'll need to let your agency know if they make any changes.
Any good agency will be willing to work with you directly to provide the correct information/authorizations needed. Don't leave it up to chance. False sense of security in radio programming isn't something you want to bite you in the arse when you really need to depend on it.