Not the answer you wanted of course, but there are very few places in the world where you don't find mosquitoes and the others are considerably further away.
New Caledonia, French Polynesia, The Seychelles, Antarctica.
While not in France, the first two of these are special collectivities of France, and the first three are French speaking. The last doesn't really have that holiday climate.
Mosquitoes exist everywhere else, from the tropics to the Arctic. Anywhere there's water to lay eggs in and animals to feed from. Large amounts of standing water tend to encourage more mosquitoes and dryer areas have fewer, but for completely mosquito free areas you're quite limited. In choosing the Camargue for a camping trip you've set yourself up for a fail on this front, it's perfect mosquito territory, you'd be better off just about anywhere else.
n.b. That doesn't mean these areas don't have biting insects (midges etc), they just don't have mosquitoes.