Usually the Simplex freqs. used in conjunction with a trunked system are conventional 800 MHz freqs. - no pairs. Here in Portland there are 20 including the 5 WA state freqs.
There are 5 for fire, 5 OR, 5 WA and 5 national.
Unless someone has a list, you can find them by searching the FCC database. You need to put in the exact licensee name, like, perhaps, "King, county of".