I have an idea that just may be a good one. Stay with the forum, post to threads and ask as many questions as you need to ask. Over time you will figure out which members live near or fish that area. Then (if I were you) I would ask via PM to some guys who are there where they think will be best when you are going to show up. if the trip is all about fishing the Park may not be the best destination. I've been and didn't find it to be outstanding but outside the park in both Wyoming and Montana there were more opportunities than I can remember.
Fly shops are cool and if you have no local folks to help you they are a whole lot better than no guidance at all. You gotta figure, at a shop you will get the same advice as the guys who held the door for you when they were leaving as you came in......... Unless you hire a guide from the shop, there is common knowledge advice and there is proprietary advice. What you want is the proprietary kind. You need a local for the real inside info, it's time to make some friends