I bought an Ase Utra Jet-Z CQB in Finland, which is a pretty quiet can on a 5.56, but heavy. I got it for 400e I think, and sold it for the same, no paperwork required at all. I would be arrested and face up to 10 years in prison in the US for such a heinous act against humanity! I guess we should regulate mufflers on cars...oh wait, we do. You HAVE to have one, or face citation and fines.
I don't know of any specific 6.8 suppressors in Europe, but there are plenty of 6.5mm suppressors from Ase Utra, since 6.5x55 Swede is such a popular cartidge there.