Yeah friends are great sources for this. I ask people all the time if they have classic games and systems they don't use. I've gotten plenty of freebies or cheap pickups this way. CraigsList is also a really good resource..or use the buy/sell/trade forum here. Also knowing other local collectors comes in handy, I know a few guys and gals that collect and are always looking to trade and also we keep an eye open for one another when out and about at thrift stores and such.