My ortho surgeon sold it to me.

My hospital gave me the Donjoy Iceman Classic, though I probably paid for part of it. There's a well you put some water in and then four frozen water bottles (with some water taken out so they don't split in the freezer) are added to keep the circulating water icy cold for a few hours. I found 4 bottles was way too cold so later in recovery, I only added two new ones that were frozen solid.
I'm at 10 weeks out from TKR and still use it after walks. I sometimes lie on the pad that has circulating cold water for back pain too (another problem of mine.)