Specifically, it's in a place called "La Maddalena", much closer to Chianciano Terme than to Montepulciano and Monticchiello, actually. It's still in the Siena province though.
Here's the precise location:
This is the only phone contact I know of, along with the address:
°°° CONVENTO DEI PP. CAPPUCCINI LA MADDALENA - Montepulciano - Via dei Cappuccini
Hope this helps.