Local bottling plants and distributors usually have the license and supply the stores. Try the old-fashioned yellow pages under Bottling Plant, maybe?

It's Schweppes, I think, that still makes/licenses the Diet Tonic Water, though I've only found it retail in a very few places (local grocery chain called Western Foods, for instance), and possibly the Real Canadian Superstore (Loblaws's out East).

You from the Yukon, Maggie?! I used to live in Whitehorse, about a century ago