Here is what I do... go to the on line yellow pages, type in your location and search for "Seed Supply"

A few that come up for your area:

Fisher Landscape and Golf Supply 519-652-6752

Ontario Growers Supply 519-641-3992

Fingal Farm Supply Ltd. 519-769-2070 (in Union?)

I usually have good luck at the Farm Supply Stores. Call ahead, if they don't have it in stock, usually they will order it for you.

Can't say for Ontario. You might get lucky and find some for sale in a nursery (but probabaly not a big box nursery). I happened to come across 40 pound bags in a local nursery around here and bought one and then noticed they were sold out a week later. You can also buy it mail order (gas money versus postage fees is one of the economic considerations).