I was looking before and during the first couple months of the season. Not sure exactly what you are after but there might be some show up after the season is over, though your best bet is to start looking Oct-Nov timeframe - lots online then.
Use this tool --
www.searchtempest.com -- it will allow you to search multiple cities in craigslist at once.
As PD said, look at KC, OKC, Tulsa and Springfield/Joplin Craigslist sites.
Mine will be for sale hopefully later this summer - I wont want much for it - 2 hole powder coated white one.
I plan on having one of these made...(been wanting one for 2-3 years now - hope to pull the trigger soon, have had them make a couple tweaks to the design)
http://www.northstarplasticsinc.com/#dog_boxes:300E
I'm going to get the louvered doors, with upgraded latches and hinges -- no slant sides and have them add a storage locker of some sort on it plus a cargo rack. Should fit my needs quite well.
A couple months into the season a guy in N OK had a deerskin 8 or 10 hole box for sale -- think someone also had an Ainley for sale somewhere close -- they are stainless steel and NICE -- just not quite what I'd want - both were smokin deals and fractions less of what you'd pay for one new.
Id wager the guy never sold it -- I wasnt interested but if you come across that deal - snatch it up if it'd fit your needs and you have the storage space to keep it in the off season.