Prudentius, in his Hamartigenia, is not afraid to use a fifth-foot spondee from time to time. Here are the examples I’ve come across so far, all with a quadrisyllabic word spanning the fifth and sixth feet:
76: una eademque tamen rota sideris indiscretis
266: ac velut artificis domini manus inperfectum
422: Postremum cuneum rex promovet Euuaeorum
713: imperio. Hoc mulier rea criminis exprobanti
859: ditibus et longo fumantibus intervallo