  We study the surface elastic response of pure Ni, the random alloy FeNiCr and
an average FeNiCr alloy in terms of the surface lattice Green's function. We
propose a scheme for computing per-site Green's function and study their
per-site variations. The average FeNiCr alloy accurately reproduces the mean
Green's function of the full random alloy. Variation around this mean is
largest near the edge of the surface Brillouin-zone and decays as $q^{-2}$ with
wavevector $q$ towards the $\Gamma$-point. We also present expressions for the
continuum surface Green's function of anisotropic solids of finite and infinite
thickness and show that the atomistic Green's function approaches continuum
near the $\Gamma$-point. Our results are a first step towards efficient contact
calculations and Peierls-Nabarro type models for dislocations in high-entropy
alloys.
