Judging from the list Idaspud put up your best bet would be to get one in Fairfield, it is just a few miles from where you turn off to go up to Pine/Featherville. If you want to get one in Idaho Falls the easiest would be to get off at the Broadway exit, turn left and go about 1/2 mile, on the left will be a Quiznos and right by it is the East Idaho Visitors Center, they have them for sell there.