Stumbled upon Link hidden: Login to view today, which is oddly enough not a forum but a magazine. They publish an online copy which can be viewed free at the site.
It's a typical sort of thing that one sees in flea markets and swap meets, and the info is kinda sorta useful if you're new, but what I found more interesting was all the supplier ads. When I was first doing flea markets back a million years ago, substantially all of my suppliers came from magazines like RF. Generally they're good companies, mainly US based, and while many (I gather) are selling things you might be able to get slightly cheaper by going straight to China, the shipping costs and 'pre vetting' of Chinese suppliers done by the American wholesalers are arguably worth the slightly higher per unit cost.
Some that caught my eye were:
Link hidden: Login to view
Link hidden: Login to view
Link hidden: Login to view
Link hidden: Login to view
Link hidden: Login to view
Link hidden: Login to view
Link hidden: Login to view
Link hidden: Login to view
Note that, of course, some of these may already be in the Salehoo directory.
Frank