I'll second the use of antenna search. It's very helpful because the radio user may not actually be the licensee. (As some users hire communications firms to handle licensing, repeater installation, etc.)Note also that many businesses these days use Nextel, or trunked common carrier communications, which do not license the individual users, so there are no FCC records at all of the individual business.
In those cases, only using close call/freq counters near the users can find the frequencies, to give you enough info to trace down the licenses.
For businesses in your local area (within 4 miles), you might try this website, which will list users and location of all FCC licensed stations/antenna sites within that range:
AntennaSearch - Search for Cell Towers, Cell Reception, Hidden Antennas and more.