I can find a lot of data about which countries currently have the most net trade with Britain, but I assume that Brexit will hit them unevenly. For instance, if a country (Germany?) mostly buys/sells heavy manufacturing to the UK, you'd expect a lag or a pre-emptive decline in trade ahead of the March deadline, whereas you'd expect a country that traded food with the UK (France?) to experience a more immediate effect.
Assuming that it will be countries that have large daily volumes of trade with Britain or trade mainly in consumable goods, or have large labor populations in/from Britain, which countries will be most immediately affected by Brexit assuming a no-deal outcome?