Doubtful, given that GMD passed away in 2008. Unless there's a manuscript hidden away in his papers that hasn't been published yet then I suspect that the other misadventures of ol' Flashy will forever remain between him and GMD.
I contacted his agent a couple of years ago. There is no manuscript about the civil war or anything else, I'm afraid. With that in mind I wrote a Flashy novel covering his adventures post first Bull Run\Manassas to the end of the third day at Gettysburg. His agent was most discouraging about it.