Gas cylinders in France

I got a bit fed up searching through pages and pages of topics looking for any discussion about this subject so I have posted this as a new topic. We will shortly be travelling through France for 3 months with our Caravan and despite having two 7kg light Calor gas cylinders we know we will run out of gas at some point. So, do we carry only one plus a Camping Gaz cylinder or is there a readily available alternative gas network in France? We are prepared to buy a cylinder over there together with the adaptor but can anyone offer any advice as to brand and availability etc?