I'm afraid you are going to find pipe shops lacking in Seattle.
Washington State would be perfectly content to run out every tobacco user.
Kirsten Pipe Co. is in Seattle. They have 2 locations (original store in Ballard -
Map1 and a new store in downtown Seattle -
Map2)
I haven't been in the newer store downtown, but I understand they cater more to cigar smokers.
Rain City Cigar has a small pipe/pipe tobacco selection as well.
http://www.raincitycigar.com/