It's all a big myth. Steelhead don't really go to sea. They grow big up in the headwaters where no one thinks to fish for them. Up in the mountains they grow large on a diet of mice, birds, and alpine crawfish before decending downstream to their spawning grounds.
You do hear of people catching them occasionally. Point No Point is one place I seem to recall hearing reports of steelhead success, but can't remember what time of year. You should pick up a copy of Steelhead Country by Steve Raymond. He devotes some ink to fishing for steelhead in the salt during the winter. He may devote some ink to the same issue in Estuary Flyfisher. I have both but haven't spent much time in the latter.
Bush point gets a lot of beach action in the winter. There are spots all over the sound that they can be caught in the early summer and late fall and winter. Those who have learned about them generally keep tight lips! It is hard earned knowledge to find those salt water spots! A person will pass up a lot of salmon and spend huge hours finding them and then even more hours figuring out how to catch them.