Are their any other causes for painless vaginal sores besides syphilis?

Yes. Bechet's disease, trauma or cuts, lichen sclerosis, or cancer can all cause painless sores.
Vaginal Sores. Sores or lesions on the female genitals are often caused by sexually transmitted infections (stis). Stis that can cause these sores include: chancroid, genital herpes, granuloma inguinale, molluscum contagiosum, syphilis, genital warts. Non sexually transmitted conditions include atopic dermatitis, contact dermatitis and vulvovaginitis.