If you find one of those I would be very interesed in what you found. I have been looking for something like that for a while...best I have found is running several day sections on differnet rivers and car camping at night
There is always a reason not to...
Main Salmon. Or is that not close enough. Certainly more alpine than quite a few of the runs I have seen in CO. Still plenty of water then.
Hells Canyon is not particularly alpine but I had a nice trip there one Oct.
I have done Hells canyon many times in October and had great trips. It is like the grand in the respect that it has its own weather. Still has big rapids. long shuttle though. but a jet boat ride up canyon can make all the diference