There are 2 Careflights: one out of northern Nevada, the other "tri-State" Carefilght, is HQed out of Bullhead City and has helos all along the river . Careflight nevada is based out of Reno. If the bird is RED and White =Tri-state careflight, BLUE and White=Careflight Reno.
Sounds like Tri-state careflight has the base in Vegas from the search I did.
Mercy Air is a subsidiary of Air Methods, the largest HEMS provider in the US
As for scanning, Tri-state uses Sat phones but carries Wulfsburg Radios no dispatch frequency.
Air mehods does not have a dispatch frequency as far as I know, however they are on a vhf am frequency in cailfornia on 131. something.....
As they are used for long haul transports in the area of 150mi or less check CCFD ch 7 and 8