Need Help in Finding Farmhouse in Tuscany!!!

Booking.com has many search filters, one of which is Farm Stays. There's also this site https://www.agriturismo.it/en/farmhouse/tuscany Many establishments will list with more than one service and have their own website and there are sometimes discrepancies of price and availability which can work in your favor.

Montepulciano is pretty far south and off to itself. I prefer to be up by Poggibonsi at somewhere close to Certaldo or San Gkmignano.
I most often use Booking.com to find accommodations.
The area has hundreds and hundreds of farm stays. Find a city you want to be close of. Then go to Google Maps and sign into the town. Then hit the +/+/+ a few times and little bed icons will pop up indicating places to stay. Then click on the icon for info.

We stayed in Arezzo and found it convenient. Montepulciano seems far away and less central. Look at Karen Brown's website for places in Italy.

We stayed near Montepulciano for two weeks on our first trip and found it to be ideal for us. Our second trip, also two weeks, we wanted to stay in an old town rather than in the countryside and picked San Quirico. That was also an excellent location for us.

Read the tour books etc and decide on the area you want to be in. Then start looking as the above replies suggest. In our case the places we rented were one week, Sat to Sat, minimum so that's something to consider.

You could even move over towards Assisi instead of Tuscany. We just booked a farm house there for next summer. The area is just as beautiful, less busy and a little less expensive. (Have previously done both areas)

Poggio Etrusco is just outside of Montepulciano. Great apartments, lovely hosts, breakfast served in your apartment. Very peaceful.

I have stayed at Villa Nottola http://www.villadinottola.com/eng/#!/page_splash outside of Montepulciano. It was wonderful, quaint rooms with a restaurant and pool on the grounds and all you need. Very kind hosts. I highly recommend!