tirerack.com does international shipping and carries the real deal.
otherwise, if you look at the wheel:
See around the middle there's writing that's made of raised lettering? It should have the Breyton Logo, have the model of the rim, have the TUV certification, and maybe one or two other things written on there. If it doesn't, it's not real. It should also come with real breyton center caps, I guess
Other than that, I'm not sure there is any other way to tell. Maybe to weigh the rim, because a cheap knockoff would surely weigh more than the relatively lightweight real breytons.