The UK is still under lockdown. That said, post is working between here and Europe and here and the US because they haven't stopped trade (the opposite). Post offices are also open and the mail system is working here (albeit they're stopping deliveries on a Saturday from this week for some reason).
However right now we are on essential journeys only, which means taking items to the PO (or anything else) is not really essential. It would probably only be considered essential if you were sending some supplies to a family member who couldn't get things.
The country with the least restrictions in Western Europe appears to be Sweden, I am not sure what their regulations are about shipping but that might be your best bet, to find someone in Sweden who can do the transaction for you. Sweden is an EU country so in normal terms it shouldn't be an issue but they also don't use Euros which maybe would make it more complicated.
Good luck.