So far, the best places that I have found to purchase postcards is the newstand at Pike Place Market – at the corner of 1st & Pike. They have a great selection of view, map, and humor cards at reasonable prices.
The second best place is Juanita Bay Pharmacy (13520 100th Ave NE # 90, Kirkland, WA 98034). They carry touristy postcards, but also Tom Haseltine postcards which are far superior.
Other places that I have found to have a minimal selection of touristy cards are: Fred Meyer, Walgreens, Bartells and the newstand at Crossroads mall.
Do you know another place in Seattle to buy postcards?