I worked at a teen clinic with a really awesome pediatric and adolescent gynecologist after my M1 year. She did have adult patients as well, and some of her surgeries were the normal hysterectomies, etc, but she did have a large proportion of surgeries on younger girls for vaginal septums and other congenital abnormalities.
I think she did her training at Brigham and Women's Hospital, so maybe that can give you a lead.
Its a 1 year fellowship and there aren't a whole lot of programs out there that offer it. Louisville & Brigham are two that I know of. The specialty deals with such things as:
Ovarian masses, cysts and tumors
Menstrual disorders in teenagers
Vaginal agenesis (surgical/nonsurgical creation of neovagina)
Gynecological care for the pediatric adolescent patient
Preventive gynecologic care