We're going to be in Sarlat in late September/early October. We'd love to tour Lescaux, of course, but would love to find a guide (English speaking) for another, less popular cave. We contacted one but he's fully booked already. Any other tips for activities and restaurants in that area and season are welcome.
I'm a bit confused by your query. We've toured many of the southern France caves - - admittedly quite a few years ago. The visits were always with a guide who worked there. What would be the purpose for hiring an outside guide? You should add a visit to L'Abri du Cap Blanc to your itinerary, as well as a stop at the Museum of Pre-history in Les Ezyies.
The obvious choice is Grotte de Font de Gaume which has their own guides and offers some English tours which you need to book in advance. I would be surprised if they are booked up this early.