Or you can do it the "Old Fashioned" way...
Look at the antenna that they are using and measure the length.
MOBILE QUARTER WAVE
18/19 Inches = VHF
6 Inches = UHF
3 Inches = 800
(These are for quarter wave antennas)
That will get you into the right band. Then you can scan the select band in segments to eventually find the frequency.
OR
You can take the easy way out and use a frequency counter and be done with it.