I don't recall the name of the vendor ... but at the Allentown ATMA show -- just as you enter through the main doors -- there's a vendor that sells books and videos. They had a stack of these books on their table -- perhaps a dozen or so. Wouldn't know if they still have any, but perhaps somebody here knows the name of the vendor and can point you in the right direction. They're a pretty steady vendor at the ATMA show. In fact, I can't recall NOT seeing them at the show over the years.
Check in with Derek too. He should be able to give you a list of places (i.e., LHS's, dealers, museums, etc..) who may be selling the book. I got the last book Henning's Trains had the other day. So they're out there -- even though the books are reportedly "sold out" directly from Derek's website.
David