Marina vN Whitman had the book in her possession so I suppose they visited her and got access to it that way. I emailed her back in 2022 about it and she said she was planning on sending it to Josh Levy at the Library of Congress to go with the von Neumann/Klara papers there but I don't know how that ended up going, perhaps the book might be there now.

In a similar fashion Vincent Ford, who was the Air Force colonel responsible for von Neumann when he was in hospital dying of cancer, published a manuscript, Twenty-Four Minutes To Checkmate, on the US crash program for ICBMs focusing on the 1953-1957 period, which obviously overlaps a lot with when von Neumann was involved in those topics. It's held in the Dwight Eisenhower Library in Kansas however it's also only available if you visit in person.

It would be a great boost to the history of science if both texts were either published or scanned and uploaded online to make them significantly more accessible to both scholars and interested laypersons.