CE Compliance exception
This answer was given before the question was changed to include wire terminals and that makes a big difference as far as I'm concerned.

Ask yourself what CE directives a device like this needs to be compliant with and, when you decide that the EMC directive is one of them, ask yourself how will you prevent EMC non-compliances when there are only wires (that make nice antennas) for input and output? After all, a switching regulator does everything it can to make nice square edges of voltage and current in order to maximize efficiency and minimize heat lost (and therefore cost).

I'm not saying that there isn't one that may be found but, it'll probably cost significantly more than the cheapo ones from China.

Another possible thing to consider is that a buck converter with input and output leads is probably regarded as a "component" or sub-system for installation into something else and, just as the switching regulator chip isn't required to be compliant, maybe the products you refer to are also viewed the same way.