Start with 172.15, I think that's the most popular (or was a few years ago) with a PL of 136.5. Some stations have repeaters and have encrption on them, usually somewhere around 172.9

They have been switching to Icom F50V radios. Those 10,000 radios they have ordered (icom issued the press releases last month or so) have voice inversion technology, there's tons of downloads out there to descramble it if you want.