Try Road Race Engineering. They carry the porterfield R-4S pads, and are also familiar enough with VR-4's to know which parts you're looking for.
Plain rotors work just fine as long as they are decent quality (Rock Auto carries some decent brands for cheap). Unless you're using race compounds, slotted rotors are of questionable benefit for most modern metallic and ceramic brake pads, and they shorten pad life slightly.
The only difference between, for example, Brembo blanks and the "performance" slotted and coated versions is exactly that - they start from the same rotor.
The centric rotors are pretty good - the reason they cost a bit more is because they have anticorrosion coating, whereas the Brembo blanks do not
All in all, a rotor is just a chunk of cast-iron - the only thing that truly matters is that they are machined to a decent tolerance and balanced. Everything else is just gravy.