A very simple component which can be used to test modulation/demodulation is the MULTIPLIER component. It can be found in the Sources group and the CONTROL_FUNCTION_BLOCKS family.
I guess you can never find such an ideal component in real life, but its a good place to start prototyping your ideas.
Many semiconductor vendors make analog multipliers and mixers. Have you tried to find these components and their SPICE models?
Please look at the post mentioned above...