MDHS has an extensive collection of Blackford letters you should definitely see. Be sure to get to Carlisle (USAMHI) also which also has more letters and his diary/memoir.

ALso get a copy of Guy Hubbs' thesis on the Greensboro Guards (Co. D 5th Ala.). Hubbs has also collected several diaries and newspaper articles about Co. D and is planning to publish them, which should be a great help.