You could try the Nearly New Shop. It's run by the Junior League of Atlanta and members are required to donate. There's no set "maternity section" in the store I know of, but since the members have to donate, you might get lucky. It's on Howell Mill Rd at 75.
I have a ton of maternity clothes that I have been planning to sell but never got around to actually doing it. If you are interested in them let me know.
I think Sweet Repeats in Buckhead/Miami Circle has a good selection of maternity clothes.
2004-Started TTC; Nov 2007-Lap with endo removed; Jan 2008-Ectopic (mtx); April 2008-IVF #1 (bfp, twin girls); March 2011-FET (cp); June 2012-IVF #2 (bfp, singleton, EDD 3-19-12)
***Twin fraternal girls born at 35w6d in 12/2008***
I had success at sweet repeats and goodwill. I tried the JLA nearly new shop, and was just directed to the plus size section where some maternity stuff gets thrown in. Not much there to pick from, so not worth a special trip IMO. But it is great for good deals on non-maternity clothes, especially for smaller sizes (from the looks of the shop's inventory, junior leage members are much smaller than the average American woman!)
Re: Second-hand maternity shops?
kid to kid
goodwill
ross
Kid to Kid of Kennesaw
***Twin fraternal girls born at 35w6d in 12/2008***