Many of these departments have their own UHF freqs and dispatch them selves. There are departments that do not have UHF and are dispatched on 46.1 and 46.46. East farmingdale for example, who has UHF freqs, will tone out on 46.46 then on their UHF. Many others do this as well.
I am not sure there is a list of all Nassau and Suffolk depts that are self dispatched.
My scanner is set up is as follows. Suffolk has 11 divisions. The 11th seems to be only ambulances which I have no interest in hearing. So out of the remaining 10, I combined div 5 and 5a as one. That leaves 9 and my scanner has 10 banks. I put the 9 in and used the last bank for all the countywide freqs. I also did the same for Nassau. So for what ever area I am in and wish to hear, I will have that bank and the countywide bank running for the depts that are only VHF..