I'm no expert but I've noticed that the colors are subdued - probably because of the dyes available at the time and the 'reprints' copy that.
The first fabrics I found were the actual ones that say Civil War right on the selvage, others I got say 'vintage' or the Ozark mountains, or sometimes they say "such and so museum" .... I'm not certain of the years covered by the vintage/museum/ozark mountain fabrics but I'm making a memory quilt honoring my g-g-grandfather and he lived from 1841-1916 so that covered a considerable amount of fabric! So I'm not worried about being a stickler for "Civil War" fabric.
I didn't buy anything online, I found these all at Hancock's and a fabric place in Mobile..