Although it slipped into a few bookstores early, today's the official publication date for Star Trek: The Original Series: Serpents in the Garden. There are multiple places to buy it at that link (I'd go for IndieBound, myself). The entire first chapter is also there, so you can get a feel for the book. If you want a signed copy, you can order it from Mysterious Galaxy: San Diego and it'll be shipped after my May 10 appearance there.
However you get your hands on it, I hope you enjoy it, and I hope you'll let me know what you thought.