Grande Illusions (http://www.grand-illusion.com/) has a good selection of Civil War clothing, Civilian clothing, Children clothing, and Accessories.
Clearwater Hats (http://www.clearwaterhats.com/) has an excellent selection of Victorian hats.
Premier Clothing (http://www.premierclothing.com/) Has a fairly good supply of Victorian clothing that focuses more on the classier side of the Victorian age.
Le Ateliers du Costume (http://www.ateliersducostume.com/) seems to be an awesome French historical costume company. They make everything from poor to high class stuff in fabrics that suit the needs of the type of clothing.