  Motivated by UV explanations of the $B$-physics anomalies, we study a dark
sector containing a Majorana dark matter candidate and a coloured
coannihilation partner, connected to the Standard Model predominantly via a
$U_1$ vector leptoquark. A TeV scale $U_1$ leptoquark, which couples mostly to
third generation fermions, is the only successful single-mediator description
of the $B$-physics anomalies. After calculating the dark matter relic surface,
we focus on the most promising experimental avenue: LHC searches for the
coloured coannihilation partner. We find that the coloured partner hadronizes
and forms meson-like bound states leading to resonant signatures at colliders
reminiscent of the quarkonia decay modes in the Standard Model. By recasting
existing dilepton and monojet searches we exclude coannihilation partner masses
less than 280 GeV and 400 GeV, respectively. Since other existing collider
searches do not significantly probe the parameter space, we propose a new
dedicated search strategy for pair production of the coloured partner decaying
into $bb\tau\tau$ final states and dark matter particles. This search is
expected to probe the model up to dark matter masses around 600 GeV with
current luminosity.
