Pttersons Spawning Shrimp from Orvis. Light brown sizes 2-6, On my last trip I never had a refusal with it. If you get to experience fishing with Glister (one of the top guides)he will probably like the smaller size flies. So have more of the size 6. But he will never argue with what is working.
Also the squimp size 6 available @ the flyshop.com.
Good luck I will be there the week befor you, I'll try ro leave a few. Ask to go to the west side if the wind is right