We propose simple scenarios in which the observed dark matter abundance arises from decays and scatterings of heavy quarks through freeze-in production of an axion-like particle with a mass in the 10 keV–1 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 + \text{invisible}) at NA62. As a byproduct, we discuss the cancellation of infrared divergences in flavor-violating scattering processes relevant for thermal axion production and derive the general contribution to the axion–photon coupling from all three light quarks.