  The dark axion portal is a dimension-5 coupling between an axion-like
particle (ALP), a photon, and a dark photon, which is one of the targets of the
intensity frontier searches looking for $\sim\,$sub-GeV long-lived particles
(LLPs). In this work, we re-examine the limits set by existing detectors such
as CHARM and NuCal, and by future experiments such as FASER2, MATHUSLA, and
SHiP. We extend previous works by i) considering several mass regimes of the
Dark Sector (DS) particles, leading to an extended lifetime regime of the
unstable species, ii) including LLPs production occurring in previously
neglected vector meson decays that actually dominate the LLP yield, and iii) by
implementing secondary LLP production. It takes place by Primakoff-like
upscattering of lighter DS species into LLP on tungsten layers of neutrino
emulsion detector FASER$\nu$2. This process will allow FASER2 to cover a
significant portion of the $\gamma c\tau \sim 1\,m$ region of the parameter
space that is otherwise difficult to cover due to the large ($\sim O(100)\,m$)
distance between the primary LLP production point and the decay vessel, where
LLP decays take place, which is required in typical beam-dumb experiments for
SM background suppression.
