The vaginal orifice is lubricated by secretions from the:

The Bartholin's Glands, which are also known as the vestibular glands are a pair of pea size gland. The location of the Bartholin's gland is postrior to the vaginal orifice.

The main function of these Bartholin's gland is to secrete mucus and to lubricate the vaginal orifice. These gland is homologous to the bulbourethral glands present in the males.

Hence, the vaginal orifice is lubricated by secretions from the Bartholin's Glands.