I've trolled many times during the last week through preloved, pets 4 homes etc, and all those with potential are many miles away. Under normal circumstances I'm happy to travel to Lands End or John O Gaunts, but at the moment, due to family illness I don't want to be too far from home, hence I'm limiting my search to Yorkshire.
Mainline Border Collies is definitely a possibility, as I had Kelly (my old dog) trained by Barbara Sykes, so they're certainly worth a try.
In the meantime, any further leads greatly appreciated.