I don't think they are available due to liability concerns. A manufacturer can get certification for a specific conditions or items, however if the 'happy homeowner' installs it, the company that sold it could be liable if anything ever happened.
This would not be like someone who never replaced smoke detector batteries, and a home and those inside were lost.
I'm sure you can buy the relay's and controls and wire it yourself, but at your own risk. In our 'sue happy' world, no one wants the hassle.
Having said that, I think it is a VERY GOOD idea to have on any type of heating equipment. Safety first!