Hi MBrill,
A few independent manufacturers that I know about besides Original Mattress Factory (which I consider to be a good regional manufacturer) in or near Atlanta are …
http://www.southernnightsmattress.com/Residential.html
http://www.tuckermattresscompany.com/id51.html
http://www.ashleysleep.com/StoreLocator/storelist.aspx?countrycode=USA&country=United%20States&statecode=GA&state=Georgia&city=Atlanta
http://www.decourcyco.com/contact.htm
Some others that are not manufacturers but may be useful for mattress testing includes …
Store Locations - Room & Board Retail direct outlet for Restwell mattresses
http://www.theecoemporium.com/contact.html Carries Greensleep and Savvy Rest (a choose your own layering latex mattress) NOTE: Appears to now be closed.
http://www.mattress-choice.com/contact.php Retail direct outlet for American Bedding and Sterling & Thomas
This should give you a few “choices” in your mattress search. Feel free to post if you have any other questions
Phoenix
ADDED LATER: Post #2 here will give you some additional information about the better choices in the area.