Is there a distinct fashion aspect to tatoos, piercings and other forms of body modifications? As in fashion-as-fashion, rather than fad-style socio/politico manifestation of whatever? Can it be possible given how near permanant things like tatoos are meant to be, as opposed to seasonal, ephemeral fashion? Definitely an interesting question!
There's a book by photographer Housk Randall entitled "Revelations" which has some strong B+W studio portraits of Torture Garden type people that could be a reference of sorts for you. Otherwise, there are quite a few publications available, in which if nothing else you'll learn about things like tatoo conventions, artists to approach & where etc - but then there's this new mag http://www.sang-bleu.com/ that might be most up-market-y?
Hope this helps as a starting point.