The book "Post of Honor" consists of the war letters of S.G. Pryor, 12th Georgia Vol. Infantry.

I'd start with the "Doles-Cook Brigade" history by Henry Thomas. It gives a history of each regiment, including the 12th GA, in that brigade. Also has several war photos of the men.

The GA volume of the series "Confederate Military History" has several references/stories on the 12th GA.

The old Confederate Veteran magazine(40 volumes) would be another great source.

Of course, the 128 volume "Official Records" will have the wartime reports, battle accounts, casualty totals, etc.

Happy hunting!