Being an expert rider means absolutely nothing in the backcountry. It does not tell you if a slope is dangerous or not. Keep that in mind. As far as a backcountry traveler goes you are a n00b.
Don't get me wrong, I am not trying to discourage you, just letting you know where your head needs to be. One of the most common reasons people are buried and killed is that they have a high skill level riding wise, but have no idea on how to read the terrain they are riding. Avalanches are indiscriminate, they will kill and expert rider or the novice. Just ask Craig Kelly, Jamil Kahn, and the many other pros who have been killed by them over the years.
If REI doesn't have them, look around at the Mountaineering stores. Unfortunately I don't know who is out there in Seattle, but I guarantee there are a fair amount of them. You are of course looking for operations that carry a backcountry ski line up. Shouldn't be hard to find.
Good luck, I like that you are thinking about the dangers out there. Definitely take the course and learn all you can. Reading Staying Alive in Avalanche Terrain by Bruce Tremper is a great prep read for your Level I or basic avy awareness course. Just take it slow, experience is what you are looking to obtain and right now you don't have much. Even after the course, you'll know fundamentals but still lack the experience part. It takes a few seasons to get there, but before you know it, you'll be a competent backcountry traveler. Trust me on that one...