Lol my secret is simple. Stalk your local newspapers for lawn sales, also Craig's list garage sale section. Look every single day. Your best bet is "community sales" in older developments or even better- old trailer parks. Sometimes they specifically list video games (aka you better damn make sure you get there first) but usually you have to look for signs...pokemon, tmnt, action figures, boys toys...these are all buzzwords.
Map out your destinations strategically by when the sale opens (get there 10 minutes early) and cross your fingers.
Also- ASK IF THEY HAVE GAMES. My top finds have been people who didn't have their stuff out. They went inside "yeah I think I have some of that."
Finally, know prices and know when to walk away. Most people are completely ignorant of their stuffs value. This can work to your advantage or against you. Don't be afraid to offer less...unless its already a steal. Then don't **** with it. Buy it and run.