  We propose simple scenarios where the observed dark matter abundance arises
from decays and scatterings of heavy quarks through freeze-in of an axion-like
particle with mass in the $10 {\rm \, keV} - 1 {\rm \, MeV}$ range. These
models can be tested by future X-ray telescopes, and in some cases will be
almost entirely probed by searches for two-body decays $K \to \pi + {\rm
invis.}$ at NA62. As a byproduct, we discuss the cancellation of IR
divergencies in flavor-violating scattering processes relevant for thermal
axion production, and derive the general contribution to axion-photon couplings
from all three light quarks.
