Which lab to try depends on where you are on the planet.
Many plants operate their own lab and the technology used is likely to be a cone and plate viscometer.
e.g.
However, if the process warrants it, you can make online measurements pretty effectively as well. Upto 200degC I'd use the Emerson/Micromotion 7827/9 and for higher temps the Hydramotion dynamic viscometer.