The Ash River is on Vancouver Island near the town of Port Alberni. It is a tributary to the Stamp River. In case you arrive on Vancouver Island on the ferry from Vancouver, you ride on Highway 19 in northern direction until you reach the junction to Highway 4 direction Port Alberni. From there on, you´ll have to do some searching. The best idea would be to stop by the local shop "Gone Fishing". The people there are very friendly and will give you an up-to-date description of how to get there.
You ask first for the Stamp, asking specifically for access to Money's Pool. Upriver from there, you get to the mouth of the Ash, but even beyond there, the Stamp, too, holds some very promising spots for steelhead.
The Ash, which flows into the Stamp, has proved very productive for me, especially in February. All the fish I caught in the Ash took my pattern within the first 400 meters upriver from the mouth of the Ash. Especially the stretches of white clay are always good for a pleasant surprise. I should mention that I caught all my steelies in the Ash in winter, in the month of February. This time of the year I fish mostly heavily weighted egg flies in colors ranging from red over orange to pink. This is the only way to get the deep drifts you need. Nymphs and dries are practically not used in winter season. You shouldn´t be too surprised if anglers using spinning or bait casting equipment show up next to you in this area. On the other hand you probably won´t meet any black bears in the winter. Last not least, on the average winter run fish are larger than summer run fish.
So far, I have not yet had the privilege of catching steelhead in the Ash during the summer run. In summer and fall, the Stamp is far more interesting than the Ash - especially because there are good chances of catching them on dry flies. In my opinion, the Ash can be considered a "winter run only river" . Whereas the Stamp has a pretty good summer run, there is practically none in the Ash. You might still give the Ash a try in summer, even if you don´t catch steelies it can still be fun to watch the salmon runs.
Other rivers on Vancouver Island known to hold steelhead are the Campbell River and the Gold River, the Quinsam, the Cowichan, and finally farther north near Sayward, the Salmon River and the White River. The White River holds summer run steelhead and the Salmon winter run steelhead.