Right under the book cover graphic for each of those books at Amazon.com, there is a link that says:
Tell the Publisher!
I’d like to read this book on Kindle
For all three books that you mentioned, the publisher is Bloomsbury USA Children's Books. You can visit
Marianne Curley's page on their website and contact the publisher directly from there. The publisher will need to provide the ebook for sale at Amazon. It looks like they have released only in paperback and hardback at this point.