It took a while, but the 11th book in the Oz series is now available from Eltanin Publishing:


It includes all of the original illustrations (over 110, some in color) by John R. Neill. DRM-free.

From the Editor’s Preface:
"When L. Frank Baum began drafting The Lost Princess of Oz, he was driven by inspiration that took his writings about Oz in a new direction. Baum credits one of his young readers with the germ that grew into Lost Princess: "I s'pose if Ozma ever got lost, or stolen, ev'rybody in Oz would be dreadful sorry."

With this notion, Baum began to imagine the resulting upheaval and collective search for the fairyland’s beloved ruler. On the surface, this may seem like a straightforward story premise, but at its root this tale would be categorically different. What Baum was embarking on in this Oz book was a mystery…”

Available at:
Amazon: http://www.amazon.com/dp/B00FQ1XJQK
Amazon UK: http://www.amazon.co.uk/The-Lost-Pri.../dp/B00FQ1XJQK
Barnes & Noble: http://www.barnesandnoble.com/w/lost...=2940148462323
Kobo: http://store.kobobooks.com/en-US/ebo...-illustrated-1