Old Answer: (revised one below)
The number you are looking for is just the Refractive Index further up on the site: Edit: Since this is a conductive material, the Reflectance value is actually the correct value for a dielectric approximation of a conductive material.
^^^ not correct!
As long as the material you are creating is dielectric, just plug this into a Fresnel node, and you should be good to go. Custom RGB Curves are not physically accurate and will not give you what you want. What it looks like:
Note: I have seen tutorials that say that Blender's Fresnel node isn't accurate,
and that you have to do various things to the normal input to make it more physically accurate (Edit: as Ibalazscs said, this is only when taking into account roughness, and this method is also correct.). I tested this by creating a group of Math nodes with the Fresnel Equations and comparing it to the Fresnel node. They look exactly the same:
The above answer was just for dielectric materials. The question was asking for conductive (metallic) materials. After looking through some code and reading this page from the Developer site, I found that Blender only has partial support for conductive Fresnel. It appears that it was going to become part of the Cycles node system, and then was abandoned. The developers did include it, though, as an OSL shader template, so it can still be used.
To use it, first enable Open Shading Language under the Render settings. (Note: Using OSL for this slowed down my render times a bit.)
Next, open up a Text Editor. Click on Templates > Open Shading Language > Fresnel Conductive.
In the Node Editor, add a Script node (
A > Script > Script). Select the text file you just created (
Now, here's the tricky part. The IOR of a conductive material is a complex number in the form n+ik. Not only that, but it changes depending on the wavelength of the light hitting it, so the IOR is different for different colors of light. This OSL script takes only three IORs and interpolates the rest with a spline curve. It is still a good approximation, though. Onward!
Using a database like refractiveindex.info, find the complex ior for three different wavelengths of light, probably red, green, and blue, or about 0.68µm, 0.55µm, and 0.40µm, respectively. Plug the red, green, and blue values into the red, green, and blue slots of n and k on the node. My final node setup (using the Chromium values) looked like this:
Although this is an imperfect workaround, there is hope! There is an open developer page on a Metallic BSDF that would do all of this better and just built in.
Sorry that the initial answer wasn't what you were looking for. Hope that this helps more.