Viscosity is not affected much by pressure except close
to rarefaction.  (This is why you are not finding any handy
tables of viscosity versus pressure as you do for temperature.)
To see the effect of pressure on viscosity for the cases of slide
and squeezed film damping, look at the papers of Timo Veijola,
who has done a great deal of very useful work in this area.
The "effective" viscosity, for which expressions are provided
in these papers, is notional, not precisely a fluid property.  It
is a characterization of fluid effects that can be lumped as
viscosity for these particular flows.  You cannot take these
expressions and use them in other contexts.

--
F. T. Korsmeyer, Ph.D.
Principal Engineer & Manager, Field Solver Development
Coventor, Inc.