Nomad is right, Blaine County is your best bet. Up Ohio Gluch on your left. Can't miss it. Call first, because they are only open a few days a week and the hours can be pretty limited. It is open to the public, and there is a fee of some sort but it was not bad.
I went there once with my GF at the time (now wife). She had inherited a couple of doubles and we wanted to "try them out." I'd shot a bit of trap years ago, but neither of us had much experience with double guns. In other words, we were pretty much newbies. Nevertheless, the fellow who runs the place was very friendly, helpful and accommodating. Can't guarantee he will be there, but I think he is in charge so should be able to hook you up if you call. They can even rent you guns. I would probably join (there is a membership option) if I was up there more often.
By contrast, on the same trip we had tried to go to the Sun Valley Gun Club (for the same purpose) and were treated rather rudely. This was pretty surprising considering Sun Valley Co. personnel tend to be pretty decent. In any case, one needs a reservation to shoot there, I think it is rather expensive and one of their employees has to hold your hand the whole time. Kinda lame if you ask me. Definitely set up as a day activity for tourists rather than a facility for regulars/locals. I never see many people out there.....probably tells you something.
As far as that place south of Bellevue.....Wood River I think.....I am not sure if it is open to the public. In fact, it seems like it is never open at all except on certain Sundays when they have a whole slew of competitors around for an organized shoot. Not quite sure what the deal is with that one.
