I have some old viscosity charts that shows the typical viscosity of various products including 5, 25, 100 and 230 pen asphalt. On a semi-log graph, there is a straight line relationship between the viscosity in cSt and temperature.
I'd try doing some testing of your SR to get viscosity/temperature data and see if you get the same relationship. You could be able to curve fit the data to produce what you need.