had a client a few years back who was an actual arms & armour dealer - yep we do have them in the uk.
And he told me that for $20 you could buy a kalishnikoff and 1000 rounds of ammo in most 3rd world countries.

smuggling stuff into the uk isn't hard, we have a very long coastline.

Smuggling of arms is still a much more urgent issue than 3d printing them.