Warren, there may be a gentleman, in Queensland, who might have an interest in the document you mention, or at least in seeing a copy of the item, as he is doing much research on early photographers of Queensland, including Bennett. He is Marcel Safier, and he has a number of web sites on the subject. Let me know if you would be interested in contacting him, and I shall send him a message about this.
Also, the secretary of our Civil War Round Table in Melbourne, Mr. Barry Crompton, has a major interest in Confederate postal history, so if you wish to correspond with him, please let me know. Barry has been collecting for decades, so may have a sizeable collection of postal items.