I had my Lunasix-3 serviced and calibrated by Gossen last year. Very quick and, by the calibration certificate, very accurate once again.
The price was also pretty reasonable, especially as some parts of the dials had cracked and needed replacing. One difference is that I live in the country next door to that of the manufacturer, so transport is easy. Meters are smallish and lightish, so you could always send it to Germany - or contact the distributor that chriscrawfordphoto suggests above.