Ryzen PRO processors and APUs, support ECC. (Edit for Mark, I should have said "officially". Unofficially, they all still have ECC functionality Enabled. But only the PRO processors are "validated" for ECC usage. Think of it like a CYA warranty for workstation vendors.) (Those processors, AFAIK, utilize the same dies as the non-PRO versions, only they have extended testing / validation, to make sure that the ECC is working and whatnot.) Used for professional workstations.
I don't believe that the Ryzen PRO processors are available retail-boxed, which may be why you've never seen them. They are intended (AFAIK), to be integrated by workstation OEMs, and are purchased in bulk / tray form.