The 19th Georgia indeed carried a First National in August 1861. It was either a flag for the regiment or one of the company flags used for that purpose. This predated the creation of the ANV battle flags, which the 19th GA did use (their Second Bunting flag survives in a small museum in Jacksonville, FL), by a few months (late November 1861 for the silk issues).

Hope this helps.

Greg Biggs