While I have yet to stumble upon any 50-family yard sales, I did find the Melrose Trading Post which sports in excess of 200 vendors and takes place every weekend. Here's a photographic tour of some of the stuff we saw for sale at it this past weekend.
NEW FEATURE: "THE MELROSE TRADING POST!"
http://www.i-mockery.com/minimocks/melrose-trading-post
Enjoy!