EXCLUSIVE: The book was snatched last year after a bidding war for $5 million by Imperative Entertainment and now the Eric Roth feature film adaptation of David Grann's book Killers Of The Flower Moon: The Osage Murders And The Birth Of The FBI may end up with another few good men. We hear that Imperative is working right now to put together some A-listers for the big screen; first choices happen to be Martin Scorsese, Leonardo DiCaprio and Robert De Niro, and we hear the…