Are you sure thats the correct spelling, I know of an Italian make of motor under the name of Morini Motori, or Franco Morini. The Morini s6 is used on ktm 50, lem and cobra 50 mini motorbikes is it not? The full specs are here http://www.morinimotori.com/eng/motori01.asp
Try there for an older 28cc motor. Also the Sachs Saxonette has a very similar motor., that is availalble in Europe.May have to buy the whole motorized bike, just to get the motor & rear wheel.
Herdan in Pennsylvania sells Morini Franco Motori FM128's. My wife just purchased one for my birthday this June. If you do a search for 'Franco Morini Kickbut Engines" you will find the site. I never was able to get through by email. But if you call, you will find they are very helpful and prompt. It only took four days to recieve my engine. It does not come with anything more than the engine, exhaust and hub. You will need 12g/.105" spokes, a fuel tank (I'm using a Tecumseh small engine tank for now), throttle w/kill switch, the works. But it is a very fine little engine. The folks at Herdan sent photos of one of their bikes along with the instructions and are very willing to talk. Enjoy!
The Sachs engines were made for them by Morini Motori. The engines are now produced with Taiwanese & Japanese parts w/German bearings. The current version of the Sachs is available from 'rotorybike.com' out of Australia. But do to licensing restrictions in several countries now only has 200 watts of power (1/4hp). Sachs no longer produces these bike themselves. Parts for the older bikes can be had from 'moped.com.au' but are very expensive.