You might want to check with local yoga studios – some of them sell stuff like that. Definitely East West Bookshop though if you want to leave West Seattle (it’s 65th & Roosevelt, I think).
Thanks for the replies. I ordered one that was scheduled to arrive over a week ago and am tired of waiting. I looked at the Web sites you listed – thank you! – and will start with the local yoga studios tomorrow, and East West, Zenith, etc.