I just got a new thermostat from Graham's in the UK.
http://www.grahamsmotorcycles.com/MZ%20 ... ORPION.htm
They were most helpful, even to the extent of sending me four pictures of the part to confirm that it was the correct item, such as:
Excellent service. It cost oz$ only 38.63 incl postage to Perth, very very reasonable. I costed a thermostat off Yamaha, the wrong one, and I'd have been up for over Oz $120.00!
Use them, good value.