The distributor either went under, lost the rights to distribute or found the business not worthwhile. You can still get the bikes if you dig hard enough, but until a new distributor gets lined up, you'll have a tough time.
Their German website (http://muz.de/) has an English translation if you want to see the bikes.
Note: the main German site also lists the distributor for the states as the same company that ran mottoradna.com. Perhaps they are still doing the distribution, but gave up on the website. Give them a call and see.
I'm not completely sure, but I think MZ went under. Motorcycle-USA.com did a test of the Baghira a few months ago and as an endnote to the story said something about the major shareholding company dumping MZ or something. At any rate, I don't think MZ is operating right now. But I could be wrong. The details were few and I've heard or read nothing else about MZ since.