The Edge of Worlds is now available in ebook and hardcover, with audiobook to follow at some point soon.
Amazon US, Powell's, Barnes and Noble, Chapters Indigo, Mysterious Galaxy, Books-a-Million, Kobo, Amazon UK, Amazon Canada, Amazon France, Amazon Germany, Amazon Spain and all the other Amazons. Order it locally in the US from an independent bookseller through Indiebound. And if you want it signed and personalized, order it before Saturday April 9 from Murder by the Book.
* I have a post on My Favorite Bit about The Edge of Worlds: http://maryrobinettekowal.com/journal/favorite-bit-martha-wells-talks-edge-worlds/
* And it's in the new books round-up on Barnes & Noble: http://www.barnesandnoble.com/blog/sci-fi-fantasy/new-book-roundup-supernatural-lockup-doorways-to-magical-worlds-and-a-lost-tolkien-tale/ (It's a two book duology though, not a trilogy.)