I wrote a nonfiction picture book about a World War II story that is as jaw-dropping as it is little-known, if such a thing is possible to compare. It's called Thirty Minutes Over Oregon, and I have done a lot to promote it...even though it is not yet a book.
The story in the book and the story behind the book are here.
At times, I have followed up that post with "evidence" I encounter in my travels that I feel supports my claim that such a story (i.e. not already famous) in such a format (picture book) would indeed find an eager audience. Plus, my philosophy with all of my work is not simply to wait for an audience to find it but rather to go out and help build an audience.
Up till now, most of that evidence has come from the institutional sector—schools and libraries. I recognize that these will likely be the biggest markets for this topic.
However, I can now add a small slice of visual corroboration from another sector—Barnes & Noble. (I'm sure many independents would agree, but the industry relies most heavily on B&N's support.)