Wherever they are, and some stations outside the town are close enough to respond, additional alarms, which we don’t actually hear anymore, will call them in. Each town or municipality will have its own call-in system. Fairbanks, for example, might call in North Pole, and sometimes does, but probably never call in Anchorage since it is an eight hour drive unless the disaster is so huge it would still be unresolved the next day. For wildfires such as a couple years ago that burned millions of acres north of Fairbanks, they called in firefighters from the Lower 48, which would be beyond the old numbered alarm system.
Thanks for the explanation!