I had the same problem, could not find RENOLIT-RHF1 anywhere

The only thing that cropped up was this:
evilbay.co.uk/itm/LQUID8R-FX-1-Synth-Grease-w-PTFE-Replaces-RENOLIT-RHF-Precharge-PCP-Airgun-Pumps/271115044952

Although I would think it would be OK to use the same silicone-based grease that Hill does.

Pse don't use 3-in-1 in these high pressure pumps, it could be very dangerous!