Just read an article that mentioned this new book about Goth fashion.
Gothic: Dark Glamour by authors Valerie Steele and Jennifer Park.
While there has been many books written about the goth subculture generally (Mick Mercer alone has written four) from various viewpoints, this is the first book that mainly focuses on depicting Goth fashion. Its a coffee table book, and its about $50 USD.
Can't say much else as haven't read it yet.... but this is definitely on my to buy list.
Amazon.com most probably, as I can't find a local shop that stocks it.
There also isn't very many books that just focus on the fashion of subcultures, excepting possibly Polhemus's work - Streetstyle: From Sidewalk to Catwalk, Style Surfing: What to Wear in the 3rd Millennium and Fashion & Anti-fashion: Anthropology of Clothing and Adornment.Polhemus, also a photographer, seems to have cornered the market, and has been writing on this topic for some 20 years now.