The sources for the Fresnel texture are included in the V-Ray SDK which comes with every installation of V-Ray for Maya (f.e. in C:\Program Files\Chaos Group\V-Ray\Maya 2014 for x64\samples\vray_plugins\textures\vray_texfresnel). It should be enough to answer any questions that you have about it, but if something is still not clear, please post again.
Best regards,
Vlado