I have a good portion of Nanase's singles that ImpactBreaker posted a while back. If anyone wants those uploaded, let me know
In reference to your question, Try Olivia. And Kana. Although, to me Kana's voice is pretty irritating x_x;
High & Mighty Color has a female vocalist. But i don't know if she's really "gothic". But their music, i believe, is pretty rock-ish.