In October you might be looking at river drift boat tours rather than saltwater boats. I mean you can book either, but for the salmon run the mature ones are up river by then. There are always immature (but still big and delicious) salmon in the ocean/sound.I'm going out to Seattle in October. I kind of want to look into this now.
Salmon run fishing can be a combat sport out here. You can fish river banks by yourself, but it will be nearly shoulder-to-shoulder anywhere there is public access.
Another thing I learned after moving here is fishing regs are WAY more complicated than in Iowa, and can literally change by the day. I'd highly recommend getting some kind of guide who can help make sure you stay legal if you don't fish here often.