Does anyone know of any companies that hire pendulum slip testers? I'm struggling to find any. 

I'm weighing up whether to purchase or hire. 

Thanks in advance

And they're not simple bits of kit to use - correct setup and calibration, selection of rubber foot etc. all critical to providing usable data.  So training etc. also part of the cost.

Pendulums are regarded by HSL as the most appropriate bit of kit for measuring the slip resistance of a floor surface as it actively measures the interaction of a 'foot' and the floor in question.

Other bits of kit are around, like trolleys which are quicker to set up and run, but be mindful of exactly what you're looking to test and how repeatable you need the test to be.