Hello from across the lake! Remember the Fast Ferry from Toronto to Rochester? Haha anyway, I'm a garage sailor! Just yesterday I got five games (Mag Max, Abadox, Bionic Command, Bart vs. Space Mutants, and Ninja Gaiden with manual and poster), a few Nintendo Powers, three Commodore 64 disk drives (no cords), a Family Boy (no cords/controllers), and a super 8 camera with a super 8 film splicer, all for $10 at some guy's yard sale. I even referred the guy to Nintendo Age, so maybe we'll see him around sometime!
It's really a patience game. I'll frequently check collector stores and flea markets (about once a week or week and a half) just to see what they got in and what's changed since my last visit. Doing this will also make you a 'regular' and if you chat with the store owner about your interest you can sometimes give them your number and they'll give you a call when new inventory has arrived. Maybe that's a little too personal for you, so instead you should just keep checking. Personally, I haven't found anything too substantial in the way of rare titles in the wild, but when I do I know it'll be that much sweeter knowing the struggle that went into my search. Good luck and stick with it!