Where do you buy the exact thermostat housing that has the requires the Gates seal o-ring?

Also what brand is the housing? I don't know where to buy the thermostat housing that you can just snap the thermostat with o-ring back in to seat it. Everyone I talk to says they have never seen one that requires an o-ring. I want this specific one because it looks a lot simpler to install than the one I took off. Also the one I took off has a hole in it that's why I'm replacing it in the first place.