It simply isn't possible for any print, which only absorbs light, to produce a colorimetrically accurate and useful reproduction of the CIEXY human gamut "horseshoe."

The curved boundary represents the maximum color saturation. It is the result of a single wavelength of light between about 400nm to 700m. Along the bottom line of the horseshoe, the position on the line is determined by the relative magnitude of two wavelengths combined, 400nm and 700nm.

A print, or any physical, non light emitting object must completely absorb all other wavelengths of light.

Consequently, any continuous spectrum will have all of it's light, except those single wavelengths removed and thus won't produce a visible result.

As one moves from the horseshoe boundary inward, colors decrease in saturation and the maximum possible luminance a color can have increases. Luminance being the value of Y in linear space or, traditionally, L*, in CIELAB.

The theoretically possible saturation limits for colors at varying degrees of luminance are called Macadam Limits. Colors at those limits are known as "Optimal Colors." These are not actually physically possible since they require infinitely sharp and absolute frequency cutoff's as well as 100% in the passband. They are best thought of as a theoretical limit.

https://en.wikipedia.org/wiki/Gamut#/media/File:Optimal-color-solid,FL4,XYZ.gif

However, using emissive light one can produce colors anywhere within the CIEXY gamut by, for instance, using 2 lasers with wavelengths on the CIEXY boundary where the desired color lies on a line between the two boundary points. Adjusting the relative power of each laser determines where on the line the reproduced color occurs.