IIRC, MZ is no longer importing to the USA.
Their website still lists a US Distributor, but they don't have a US website and their email address for the US is us_costumerservice@hotmail.com
A Hotmail address for a US Distributor is not exactly confidence inspiring in my book.
On the slightly brighter side, the single cylinder MZ's use Yamaha engines, so you should be able to get parts for the engine... if you can figure out a Yamaha model that uses a comparable motor. Might be a little bit of a problem with the 660 since Yamaha doesn't import any 660 bikes, but Raptor quad motor parts might be common. Otherwise, all parts would have to be imported.