Some advertise on craigslist, facebook, Auctionzip.com. You could probably place a add on craigslist in the 'Farm and Garden" section to see if anyone knows of one. Some are only once a month, some every week, swap meets like at tractor supply do happen in a lot of area's. The ones I attend are...
Well, maybe you got a Chicken Auction with-in driving distance you can take them too. They sell Good in my area----higher than young layer hens it they are pretty and good size.