Hi - try this lot then and search the counties of interest:
http://www.lastminute-cottages.co.uk
- they list availability at each location, but the nature of most of the SC accommodation is that they work on very low margins so do not subscribe to the booking services like Hotel Connexions.com or Opodo, etc.
Landmark Trust at:
http://www.landmarktrust.org.uk/availability/l ate.htm has late avilability but restricted locations.
http://www.welcomecottages.com or see also at:
http://www.countrycottagesonline.com/Late_avai lability.htm they may have dates but search by date and location and if the property has not updated their info, then no chance of getting any success.
Farmstay is still the best I reckon - ok, so you ring the properties, but I think you will be having to do this now, even the local TIC would probably suggest this at this late stage.
have good break..!