There are two places in Longview that have the permits to sell black powder. The Gun Shop, 1023 15th Ave., 360-636-1230, is where I get mine. It's cheap, which is good, because I'm going through a lot of it. This is an old fashioned mom & pop gun shop, and they're good people.
You can also get Goex at Bob's, 1111 Hudson St., 360-425-3870. This is a pretty nice general sporting goods store, and they have a separate building with toys and housewares to keep the rest of the family busy while you ogle guns, canoes, camping gear, etc.