Buy and Sell Groups?

I think I know the usual places to get cast iron-flea markets, estate sales, Ebay, antique stores, etc.
What I'm wondering is are there any collector groups online with a buy/sell/ trade section? I'm kind of surprised I don't see one here.

Some on facebook. Other sites' forums if you're a dues paying member.

Re: here, see: http://www.castironcollector.com/forum/showpost.php?p=44051&postcount=10

Thank you Doug. I hadn't seen that and you explain why nicely.

there are quite a few facebook groups that do different formats... some allow you to post and just ask for offers... you can accept or decline any offer... some do a mix of auction with a minimum amt and time limit or 'classified' where you just state a selling price and its first come first served...
ironman, patriot, cast iron kings...

Thank you. I'll try those search terms in Facebook. I really dislike the Facebook format though and try not to go there much. I much prefer forums like this. Much easier to navigate and find the info you're after.