I got to be honest with you, if you limit your self to Seward to Denali you are going to be hard pressed to catch some Salmon. Your very best bet is a fly out with one of the flying services. Here is a link to Rust's Flying Service
. They have been in business for many years. They have one day and 3 day fly outs that would work for you.
In August the Silvers and Pink Salmon are in the Kenai river. If you want to fish the Upper Kenia River try this outfit
. You will have to drive to Cooper Landing, Alaska on the Kenia River. They can put you on some fish.
If you want to try on your own then I would go to one of the many fly shops in Anchorage and ask where you can catch some fish. One thing you could do is take a float tube, or buy one there, and try some of the lakes on the Kenia Peninsula. Alaska has some great fishing but you need an airplane, a boat or knowledge of the area. I can tell by the tone of your post you have high expectations and you may be disappointed with out some help.
The guides I have listed have been good in the past but I don't know how they are today.