I thought I'd start a quick thread listing where to get supplies locally in southern Ontario. Please feel free to comment with your favorite places and I'll add them to this list.
Flour / Grains:
A and E Fine Foods, 19811 Woodbine Ave, Queensville, 905-478-1500
Stocks some organic flour
Arva Flour Mill, 2042 Elgin Rd, London, 519-660-0199
Mills and sells organic flour directly