Excellent idea! I think it's been a number of years since the club did a Sell & Swap meet.
I would definitely partake, as I have a number of items to sell.
September time frame would be ideal for me. Probably best after Labor Day, at which point pools are generally closed, and Dunwoody Club house may be available.
I'm not a fan of the garage sale format for an audio/electronics focused sale, as everything'll be exposed to dust, it would be rather cramped, and acoustics not so great.
Also, psychologically, a garage sale setting is problematic, as few garage sale visitors plan on spending more than 20 bucks on anything. As a "last-ditch" effort, maybe. I've sold many old, outdated electronics and computers in garage sales that way, but rarely made over $25 a piece.
Advertising in in the usual places would be a must!