A few recommendations regarding publications mentioning the 21st Georgia Infantry.
(1) "Campaigning With Old Stonewall: Captain Ujanirtus Allen's Letters to His Wife" by Randall Allen & Keith S. Bohannon. Captain Allen was in Company F.
(2) The chapter on the 21st GA as found in the Doles-Cook Brigade History.
(3) Numerous references in the Georgia volume (7) of the multi-volume series "Confederate Military History" by Clement A. Evans.
Any good public or university library will have the above books.
Greg