Per IDW's front page, T&P v4 shipped THIS WEEK.
Amazon US lists it, but not as something that can be ordered from them (or even pre-ordered), but from other sellers. (not noted as being 'in stock' or when it will be 'in stock').
Books A Million lists it as a pre-order item, but no info as to when it will be available (tho you can order it).
Again, as we'll touched on this in another thread, I really wish IDW would update its website in regards to the Library of America books, as they are really the only thing I'm getting from them (Terry, Annie, Dick Tracy, etc)