The RR Database is your best source of information. NHP in the Las Vegas area uses the State's 800mhz trunked system. As to the HOT freq. question, Metro would have those units on their new non-monitorable radio system. Vegas_eric has several threads about those type of talk groups on the county SNACC 800 mhz system, they would be Henderson and/or North Las Vegas PD. Sorry there is no simple answer, but there are lots of different sites and freqs on these trunked systems, you'll have to determine which ones you can hear the best.