When something like that happens, it pretty much tells you that the publisher has removed the e-book from sale.
In this case, it appears that those e-books are changing publishers. They were originally published by Warner Books (now Grand Central) but seem to be changing to FaithWords. Both publishers are part of the Hachette empire. It looks like the pricing is going up to $19.99, too.
Because this is a Hachette title, you'll only find it at one of the major e-book stores or at the lending library. Unfortunately, OverDrive indicates that libraries in only eight states are currently carrying Birth of an Age: Michigan, Nevada, New Jersey, New York, Ohio, Rhode Island, Utah, and Washington.
I'm sending more details in a PM (the envelope in the line ahead of the Search window).