If you're moving to Paris and you worry about finding kombucha, gluten-free products, or even soap nuts, you can relax now: despite some resistance to the organic movement (in French: "mouvement "bio") by many Parisians, there is in fact such a mouvement, and thus products.
For example, an organic coop, "biocoop" has 3 stores in Paris (all on the left bank) and 5 more stores in nearby suburbs (Saint-Maur, Le Perreux, Antony, Le Chesnay, Rueil-Malmaison, Chambourcy).