Check with you local quilt shops. If they don't recommend quilters (some don't), ask if they know how to reach a longarm guild. The guild may have a listing of their members who quilt for others.
You can also go to quilt shows. Look for quilts quilted in a style you like. Make a list, since not all machine quilters will quilt for others. Since you are in Seattle, it may work real well for you to go to Innovations in Tacoma, September 16-19. It's a great machine quilting show, and you'll be able to see the work of people brave enough to enter in a major show.