Is Tonic available to buy in supermarkets?

We're off to Icmeler early Monday. Sixth visit in seven years and can't wait.
One question, we're thinking of picking up a bottle of Gin at Duty Free for the room, but is Tonic readily available in the local supermarkets?
One question, we're thinking of picking up a bottle of Gin at Duty Free for the room, but is Tonic readily available in the local supermarkets?