There's no law prohibiting sale abroad, neither German nor EU. The seller just doesn't want to.
If anyone's really interested I'd be volunteering for shipping that machine to the US or elsewhere. But make sure you prepare yourself for the cost - 10-20 kg to the US would come up to 68€.
That sounds like a great idea! How much would you charge to send it to me in the UK, though? Perhaps I could pay you in Aspirin or Paracetamol, which I may be prevented from selling to Germany via eBay due to trade protectionism by or on behalf of the company Bayer. Of course, one problem is that how could anyone be sure that you'd send them the Amiga items? You'd probably have to buy it yourself for this scheme to work, so how could you be sure you'd get back the money you paid, as well as the postage?
BTW, during the time after Commodore went bankrupt and before Escom took over, I was exchanging video cassettes, magazines and other items with someone in Berlin, but I sent him 15 video cassettes and only ever got 5 video cassettes in return. It ended when I sent him some money for a cracked Kickstart ROM, he told me the price had gone up, so I sent him even more money, then I never received the Kickstart ROM. Of course, this doesn't mean you'd do the same, but that's what can happen.