Emco/Wholesale Heating Supplies or that Woleseley address on your previous post (Hoyme dealer). Beware 8" is larger than average and you may have to buy a whole box of 50 feet which may be expensive. The DIY stores may sell up to 6". After that you have to buy it from a sheet metal shop or wholesaler.
For more Canadiana/culture check out: Bob and Doug McKenzie (you hoser). Also the Trailer Park Boys (popular in the UK for some strange reason - called Caravan Boys there?).