You might try Prorheo (sorry, you will need to find the web site from Google), Lothar Gehm was at Contaves and designed many of their instruments including the Covimat which is now manufactured by Solartron Mobrey (
so i would guess he might be able to help..
Solartron also make tuning fork viscometers which are used for various slurries.
Vann is another manufacturer of slurry viscometers (mostly for drilling muds i think)