I'm in the same area, and yeah, it's extremely hit or miss. Best chance is independent game shops, or else really going through flea markets with a fine-toothed comb. Depending on your area, I found a some OPM's in the 400 market near Barrie, a couple Game Developers deep in Dixie Flea Market in Mississauga, and some inCite magazines with a bunch of other men's interest magazines *cough* at another flea market, but mostly strategy guides at stores like Good Time Games or Microplay in K/W and Guelph. I've pulled on thing from a thrift store, a guide for Rise of Nations. Not a big find, but the price of 50 cents was OK.
I would definitely recommend collector's markets though. The aforementioned independent stores will advertise them, if not out right sponsor them, and they will have anything and everything. Heavier on Nintendo stuff, but some other magazines or guides. For this, I would recommend Brody's Gaming in Guelph, they sponsor a lot and keep a large stock of guides; that said, their staff is every bad stereotype of a game shop employee, so I try to minimize my direct shopping with them.