Since you're in Toronto, try the discount lighting stores on Cartwright Ave (near Lawrence & Dufferin just east of Yorkdale Mall); there are about 6 or 7 of them all within walking distance of each other. Universal Lighting ([url]http://www.greatlighting.com/[/url]) is one of them. Their website isn't very good but they do have a huge selection.
Start with the stores on the south side; they will have a better selection of
contemporary fixtures and you'll definitely find rectangle shades there.