Hi Kidder,
I'm not sure about Yew, but vine maple should be pretty easy to find. Something I've seen before, there are areas where roads wind along rivers through canyons and there are small strips of land between the road and the river. Sometimes vine maple will grow in these sections and road maintenance crews have to come through every couple years and cut them down to the ground. These areas make for GREAT places because there is a strong root system that will send up a fast growing sapling that tends to have few branches and grow fairly straight. You might use google earth street view to check areas of interest before you drive out. You can usually spot a maple tree even with the not so great photos due to the leaf shape.
I dont live out that way, but I'm up there almost every summer to visit family, or I would go with.
Also, I lived up in Spokane for a few years. There might be maples and yew up in the selkirks around newport, not sure though. You probably already know this, but you do have service berry, wild plume, and wild apples up there(all over the place), they make good bow wood. I could point you to a specific location if you are interested in apple wood.