Looking for AirBNB or chateau in the Loire valley

try gites-de-france.com or gites.com
Most will just be homes, but you might find agritourismes there, too

We recently stayed at Chateau d'Artigny in Montbazon for two nights, and ended up wishing we could have stayed longer. The grounds are simply stunning (or at least very nice, I wouldn't compare them to the grand chateaux). The main building has a regal main hall and staircase. The breakfast room was flanked with floor to ceiling windows that faced a canopy of trees that seemed to go on forever. While half a mile from the little town we couldn't see the town and thus it felt like we were far removed. Our junior suite was, admittedly, a bit frumpy and in an auxiliary building, but the bed and all was certainly comfortable. d'Artigny is about 45 minutes from Chenonceau and about equal distance from Chambord. We enjoyed the place so much that we skipped going to Chambord the second morning and stayed put to soak in the peace and quiet.

These are generally premium properties with offerings for groups in the Loire Valley.

https://www.demeureschateauxhotels.com/
http://www.au-chateau.com/
https://www.grandesetapes.com/
http://www.relaischateaux.com/
http://www.slh.com/
http://www.wimco.com/

Terri,
I second gites-de-france. We have found places for varying lengths of time and have never been disappointed. We also have good luck with Booking.com. Just be sure to narrow your search by putting in your filters.