So this gin soaked Brit needs to know, is tonic water a commonly available drink in e.g. 7-11s, Lawson, etc? Staying in Ginza area. Pondering a bottle of duty free gin on my way over, but need the tonic, obviously If it does exist, are they western brands (Schwepps, Canada dry) or Japanese own brand? Do they call it tonic water or something else?

Thank you