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To have a temporary SIM card in France, you'll have to buy:
You could buy the SIM card online but I guess you don't have an address in France. You can't buy SIM cards in any store, but there are many stores in which you can buy them (supermarkets, tobacco store, carrier's store). Then you can buy the refill at the same places. Some carriers even offer the option to get the refill on the internet or at ATMs.
A few examples are SFR, Bouygues, Orange, Auchan, NRJ Mobile. I'll edit my answer if you need more specific information.
A sidenote on the French bureaux de tabac: these stores sell tobacco, money games, magazines, prepaid cards, coffee, sweets, among other various products and services... You'll recognize them by their sign outside the door: