If this is a simple system (two spur gears, two bearings on each shaft) then it's trivial to calculate the gear mesh forces, assuming you know the working pressure angle, and convert them into simple bearing reactions.
For more complex systems, we use our own software (shameless plug):
http://www.ricardo.com/en-GB/What-we-do/Software/Products/SABR/
which produces a full set of casing reaction loads (including tilt moments, from shaft deflection and non-linear bearing stiffness) for each loadcase; we then apply these loads to the casings in the FEA.
