Ah... Voltage Regulators. You should perhaps edit the title, I was puzzled, since "VR" is the component abbreviation for 'Variable Resistor'.
Series Voltage Regulators -no, not how you describe it. There's only one input per regulator. They can be 'cascaded' to achieve higher vooltages (eg 48V from 24V revulators), but one will always be handling the current. The second will only be a reference for the second.
Parrallel: bad idea. They will probably start to pick a fight about who wants the higher voltage. It's like connecting the outputs of two audio amplifiers together. I highly suggest that you don't do it. You should use summind greistors, but then you lose some regulation, so...
The best idea is to use a higher-rating regulator, or feed a pass transistor, or do what manufacturers do, and build a discrete regulator.
Keith