Finding a 12 V Peltier module that reaches less than 0 °C on the cold side
They can't tell you how cold it can get because that is a function of how much you are trying to cool, and the difference (Delta T) between the inside (cold side) and the outside (ambient) air temp. 

Also how well the 2 sides are insulated from each other. That is how good the insulation of the cooler box. 

The Q is how efficient the module is at doing its job of cooling. If you have a small space to cool, and the external heat sink is exposed to a cool day as opposed to hot, you will get a much lower internal temperature. 

The Peltier you purchase may not come with a fan. If not,
be sure to include one to cool the heat sink. You will get poor efficiency without one.

The better the cooling of the external heatsink, the lower your inside will go.