They aren't in Atlanta but close by at Atlanta Motorsports Park http://www.discoveryparts.com/
They should be able to assist you with a helmet.

Bill

 

Main differences between a M class and SA class helmet-

1. Multiple impact rating (SA) for roll bar/cage protection. M has single impact rating.
2. Visor is much tougher at a higher rating for object intrusion/impact and hardware for visor attachment is rated much higher also (usually metal not plastic).
3. Smaller eye port vs M class for more protection. Even the large eye port SA helmets are smaller than most if not all M class helmets. M class full face helmets are cut higher above the brow to compensate for sight line on a sport bike, SA class helmets are cut lower because no such problem exists for automotive applications.
4. Nomex liner (SA).
5. SAH rating is Hans ready/compatible/predrilled/preanchored. Almost all SA helmets come predrilled now, in 2005 it was more rare, in 2000 it was nonexistent. M class obviously has no Hans anchor points.
6. SA class helmets usually preformed foam inside for microphone/communications system. M class, almost never.