Hmmm, well, I have more than one. I have two large ones and three small ones bought in Canada, a gargantuan one and at least three mid-sized from the US (because I tend to forget to bring mine when we go to events, so then I just buy a new unfinished horn and make a new one), and I have a couple of different sizes from Sweden. I also have bone cups. They suck, but none the less, I have them, my kids drink from them and they are finished exactly like a hirn, and they were a gift, purchased in the US, but probably made somewhere else.
We use a bunch of bone and antler products when we do the Viking demos (knife handles, needle cases, beads, hair pins, shuttles, lucets, spoons, jewellry, frogs and button decorations...you name it!), not to mention a whole pigs skull that I've defleshed, and we also use a huge amount of pelts (anything from sheep skins to cowand deer hides and bunny skins). This stuff has traveled back and forth to Europe and monthly to and from the US and I've never once had a problem at customs. Breakage and the wax melting in the horns, yes, but the customs give us a worse time trying to get our tents and slat beds into the US than anything else. They don't give a rat's ass if we bring swords, 13" seaxes, ballistas, bows and home brew, but soft wood lumber, even if it's a bed frame, WATCH OUT!