Ill echo the flea markets, there is one that was my secret stash that I used to go to but its dry now and has been since the beginning of summer. A PNT owner goes there every Saturday and buys everything up, he also made deals with the dealers to call him before hand. Before this happened though I found
Virtual Boy - $5
Super Famicom DBZ - $3 cart only
Ogre Battle 64 - $3 Cart only
Atari Lynx with California Games - $3
Amiga CD32 with Britannica - $10 - My WTF is this find, I have never seen one before or since
Steel Battalion Controller and Pedal - $10
Model 2 SNES - $5
Model 2 (top loader) Nes - $3
Various games and consoles
I had a streak where I found a rare / hard to find counsel each visit, for a place I went to maybe 10 times max, I did very well.