For a Canadian based marine fabrics store you can try;
JT'S Top Shop - Professional Boat Top Makers
I don't know if they sell sail cloth but I have purchased sunbrella from them in the past, excellent service.
For amateur, do it yourself, sail design try;
I have downloaded/installed it myself and gone so far as to trace out panels on brown paper, just for the fun of doing it. It would be worth looking into if you decide to try building one yourself.
I am with you on the attitude far too many local Kingston businesses tend to project, it gets tiring after a while. I haven't dealt with Kingston Sail Loft but plenty of other businesses here in town. Enough that my preferred method of buying locally has dimensioned quite a bit over time.
A couple of years ago I ordered a new mainsail for my Contessa 26 from Lee sails, via the Canadian rep, Bob Dryer is his name if I recall correctly. Over all I was happy with the process, a quality sail and much cheaper than locally. A few minor issues that had to be resolved but overall I was pleased with the experience. FYI you can get a cut rate if you wait until October to order. If I were to do it over again I would find a time when Kingston Sail Loft is less busy and have a serious chat with them. They do make a quality product, and I would like to have a serious discussion with a sail-maker about buying a fully batten-less mainsail, something you can't get from a mail order. With that said If that didn't work out I won't hesitate to call up Less Sails given my experience to date.