I think your best bet is a large campsite frequented by regular tourists if you're looking for Calor, I wouldn't expect it to be cheap either.
Personally we went to the Carrefour (or almost any petrol station) and bought the largest bottle that would fit in our van cupboard, they then give you a regulator. It was much much cheaper than you'd pay in the UK even if you won't get chance to return the empty bottle.