You can easily access rivers around Forks from bridges. There are also a few WDFW fishing access sites to access the rivers, and you can also access the rivers at the salmon hatchery on the Sol Duc and the steelhead hatchery on the Bogachiel. Plus, access on the Hoh in the national park is easy as is access on the Queets in the national park.
There are no fly shops in Forks, the closest one is Waters West in Port Angeles. Dave Steinbaugh, the owner of it is very knowledgeable and a good guy to check with.
Camping is easy in the Forks area with a state campground a few miles south Forks on Hwy 101 that is right on the Bogachiel River.
On the Sol Duc River there are several campgrounds: 1) about 21 miles east of Forks on Hwy 101 at Snyder Creek; 2) at Bear Creek (about 14 miles east of Forks on Hwy 101; and 3) at Sapho between the bridges on Hwy 101 (about 10 miles east of Forks on Hwy 101.
The Calawah River has camping upstream (east) of Forks at the confluence of the North and South Forks. Take the Forest Service Road near the saw mill to get to this.
There is camping on the Hoh upstream of Oxbow (east of Hwy 101).
There is camping at Mora near the mouth of the Quilleute River in the national park.
And you can camp pretty much anywhere in the national forest if you don't need or care about things like an outhouse or water source.
In mid-September you will find coho, summer/fall chinook, summer steelhead, and searun cutthroat in the rivers. Any of the standard summer steelhead flies, both dries and wets - including some low-water dressings, work for steelhead and often produce a searun cutthroat as well. I wouldn't go to the Forks area in September without some Lemire Grease Liners in both black and burnt orange tie on #6 hooks. Also, I wouldn't go there without some Lady Caroline Speys in #5 and also tied low-water style on #6 and #8 hooks. Just make sure you have wet flies in bright, medium, and dark coloration and you will be fine for steelhead.
Borden's Special, Knutsen's Spider in black, hot pink, or yellow, Kinney's Reverse Spider, and the old trout wets with yellow in them work well for searuns. Fuschia bunny leeches for coho and chinook and Flash Flies (they used to be called Karluk Flash Flies) in hot pink, blue, or purple work well for coho.
Also, a local OP pattern Don Kaas of Port Angeles originated work well for coho and steelhead, it is called the blue & purple pheasant. Don originally tied it with blue peacock breast feather hackle, but it is now tied with blue phase Chinese pheasant rump.