Reddit reviews Chief Seattle and the Town That Took His Name: The Change of Worlds for the Native People and Settlers on Puget Sound

If you're willing to do some digging, you might want to contact the

Department of American Indian Studies

at University of Washington. If anyone knows of good resources for you, they will. That teach that stuff for a living and they know so much they even offer Masters Degrees in American Indian Studies.

I know there's quite a few books on the Native Americans of Washington state. A simple search of Amazon.com should locate them. University library librarian can locate such books too. Public library not likely to have much but might have a book or two on Pacific Northwest Indians.

Finally, Google search results for "Duwamish Tribe"

History page on Duwamish Tribe website (contact info there too).

Wikipedia page on the Duwamish.

Browsing Amazon turns up these books;

Chief Leschi, War Chief of the Battle of Seattle and the Puget Sound War, 1855–56

Native Seattle: Histories of the Crossing-Over place

Chief Seattle and the Town that Took his Name

The Indians of Puget Sound: The Notebooks of Myron Eels (eyewitness accounts of Indian life from 1874-1907)

The Mythology of Southern Puget Sound: Legends Shared by Tribal Elders

Unfortunately the best histories written about Seattle are getting so old they are becoming a part of history themselves. Here are a couple of more recent additions:

Chief Seattle and the Town That Took His Name

Too High Too Steep: Reshaping Seattle's Topography