Georgia is one of the best states for shooting 3-Gun. No hotlinks since i'm on a phone.

check georgiaipsc.com for a quarterly shotgun match.

Google Creekside shooting range to see matches put on by Joe Harris.

Cherokeeipsc.com discussed hosting a regular shotgun match.

RBGC practical shooters hosts shotgun pistol and multigun matches.

EAgunclub.com hosts regular multigun/shotgun/rifle matches.

Check out Brianenos.com/forums for more listings and get on every mailing list for the clubs above (many of their sites have signup boxes - in addition to that, they'll take your email at the club).