Very few 'hard' numbers of this kind are available, particularly not for Confederate commands and especially not for civilians.
Presumably the term 'civilian' in your question includes slaves and well as the free populace. Would the term 'casualties' in your question include slaves who drowned or died of malnutrition attempting to follow Sherman's army?
To try to answer your question, just suppose that soldiers entered a home and made demands for food and any valuables on the place. When responses of family members prove unsatisfactory, some of the intruders abuse an older slave in an unsuccessful attempt to procure information. The slave dies a few days after this incident.
Today anything of this kind would be reported to the authorities and published in the media. But in 1864, what authorities would be available for such a report? The sheriff (and deputy Fyffe) would have been overwhelmed by the magnitude of the disaster to his county, state officials almost equally so. Military authorities operated according to a different set of priorities, although some Georgia civilians addressed their complaints to U.S. and C.S. officers.
Here's another question that beset the citizenry: are some of these intruders really Confederates who are supposed to be protecting us from the enemy? Enough Georgians complained about this to the War Department in Richmond that an officer was sent to review conditions in Wheeler's Cavalry and offer suggestions to correct any disciplinary problems. He determined that discipline in this command had been lax and various abuses occurred as a result.
Several books have been written about Sherman's March and its impact on the civil populace. You may wish to review these. Some minimize the harm done to civilians, such as the professor from Miss. State on History Channel who declared the worst result for most people to be loss of food supplies for a year or so. [If I've misquoted the gentleman, someone please correct me.]
Question for anyone of average intelligence --
What usually happens when human beings are deprived of nutrition for an extended period of time?
In the aftermath of Hurricane Katrina, how would the public have responded if an official at FEMA had made such a remark?
Please forgive me for straying from your question. Should you find a figure in print or hear a number for civilian casualties, please question the sources. We frequently hear different figures offered for civilian casualties in Iraq, usually with no supporting documentation. Any responsible citizen should question them, just as I'm suggesting that you critically examine any figures proposed for civilian casualties during Sherman's March.
This side of Heaven, I don't believe there's any way to get a real answer to your question, but I wish you well in this search. You should expect to find diaries, letters and memoirs at the Georgia State Archives which mention such incidents. Should you decide to visit the Archives in search of evidence, plan to spend quite a bit of time reviewing correspondence received by Governor Brown durnig this period of time. Time invested in those files should prove quite fruitful.