Dreamcatchers have nothing to do with local native culture, so the Duwamish Longhouse would probably not be a good place to look for them. Last few times I’ve been there I haven’t seen any, although they do have a very nice selection of gifts by local native artists, some of which are sold tax-free because they have been donated by the artists so the cost is a direct donation to the tribe.
I have seen them at Many Moons from time to time.