Nevermind.

http://www.ingersollcenter.org/CommunityResources has a list of some doctors near Seattle that may be able to help with HRT, but it only produced 3 results.  I don't know that any are endos, but that isn't a firm requirement.  Your therapist also shouldn't need a specific name for the letter.

This: http://www.ratemds.com
is a website where patients of different doctors can go and rate their experience with their doctor. Although, one wonders if some of the reviews on this site are made up by colleagues of certain doctors just to give the impression that said doctor is better than he or she really is.

Anyways, according to this site, the top 3 rated endocrinologists in Seattle are Dr. Frances Broyles, Dr. Dace Trence, and Dr. Shannon Heitritter.
Good luck.