Here is some general advice that might help you to find the frequencies you want. In fact, this would apply to finding almost anything.
Scan all of the VHF Marine channels.
Scan all MURS/FRS/GMRS channels.
Search the "business" bands for community repeaters and/or simplex channels that might be used by the targets of interest.
It is probably best to do these things separately at first and build up a list of possible frequencies in each set. Then try cross-monitoring for related traffic that might appear on multiple frequencies. This is easier if you have more than one scanner, but still possible with only one. Developing the ability to recognize voices over the radio is extremely helpful in this phase.
You can narrow your search somewhat using the FCC ULS database, but it takes some practice to develop an effective search technique there. Also, people who use transmitters that are licensed to radio shops do not have to have their own callsigns, so they won't appear in the FCC's records.
David T. Stark
NF2G WQMY980 KYR7128