The dress isn't black, but it's very well done. All about sims has a series of NPC outfits.
http://www.all-about-style.com/themes_npc.html Perhaps it could be recolored.
There's a maid w/ black dress here, but not a full apron http://www.all-about-style.com/vadult_feca.html
Or the Dickens casual dress might suffice? http://www.all-about-style.com/vadult_feca9.html
Their clothing always looks good in my game.