Saw those in many places last year, but always colors, never white. You could spray paint them with Fusion.

I've never seen those - however, at home depot, I saw just the "hook" part - and you use it to convert an existing container to hang over a balcony.
http://www.emilysplants.com/My_store_pages/adjustableflowerpotmounts.html

Also

http://www.emilysplants.com/My_store_pages/universalbracket.html

I saw some today at the dollar stores. I've found several nice size pots for just a buck or two...