I found another two convicted vestals mentioned by Livius, apparently quoted from Q. Fabius Pictor.
Do you remember DXXXVIII AUC (216 BC)? That bad year of Cannae plus a couple of added disasters?
Yes, you're right... the vestals were to blame for!
Right again! The convicted were plebs.
But that wasn't enough... (Ab Urbe Condita, Liber XXII, Ch. LVII:
"For, over and above these serious disasters, considerable alarm was created by portents which occurred. Two Vestal virgins, Opimia ("2") and Floronia, were found guilty of unchastity. One was buried alive, as is the custom, at the Colline Gate, the other committed suicide. L. Cantilius, one of the pontifical secretaries, now called "minor pontiffs," who had been guilty with Floronia, was scourged in the Comitium by the Pontifex Maximus so severely that he died under it. This act of wickedness, coming as it did amongst so many calamities, was, as often happens, regarded as a portent, and the decemvirs were ordered to consult the Sacred Books. Q. Fabius Pictor was sent to consult the oracle of Delphi as to what forms of prayer and supplication they were to use to propitiate the gods, and what was to be the end of all these terrible disasters. Meanwhile, in obedience to the Books of Destiny, some strange and unusual sacrifices were made, human sacrifices amongst them. A Gaulish man and a Gaulish woman and a Greek man and a Greek woman were buried alive under the Forum Boarium. They were lowered into a stone vault, which had on a previous occasion also been polluted by human victims, a practice most repulsive to Roman feelings.
When the gods were believed to be duly propitiated, M. Claudius Marcellus sent from Ostia 1500 men..."
Compare it with M. Plutarchus, Vitae Marcellus, Ch. III, sec. III-IV:
"Their alarm was also shown by ... the extraordinary sacrifices which they made to the gods. For though they have no barbarous or unnatural practices, but cherish towards their deities those mild and reverent sentiments which especially characterize Greek thought, at the time when this war burst upon them they were constrained to obey certain oracular commands from the Sibylline books, and to bury alive two Greeks, a man and a woman, and likewise two Gauls, in the place called the "forum boarium", or cattle-market; and in memory of these victims, they still to this day(late I Century AD), in the month of November, perform mysterious and secret ceremonies."