You may know by now that a book of Bingham's letters (both private and public letters to newspapers) was published by The State Historical Society of Missouri in March of 2011. It includes the May 6, 1862 letter quoted in this thread, as well as numerous other related letters. The book is published in both hard and soft cover ($25 and $35) and is available from the Society's website.
Joan Stack,
Curator of Art Collections at The State Historical Society of Missouri