  In the search for a monochromatic peak as the signature of neutrinoless
double beta decay an excellent energy resolution and an ultra-low background
around the $Q$-value of the decay are essential. The LEGEND-200 experiment
performs such a search with high-purity germanium detectors enriched in
$^{76}$Ge immersed in liquid argon. To determine and monitor the stability of
the energy scale and resolution of the germanium diodes, custom-made,
low-neutron emission $^{228}$Th sources are regularly deployed in the vicinity
of the crystals. Here we describe the production process of the 17 sources
available for installation in the experiment, the measurements of their alpha-
and gamma-activities, as well as the determination of the neutron emission
rates with a low-background LiI(Eu) detector operated deep underground. With a
flux of $\left( 4.27 \pm 0.60_{\rm stat} \pm 0.92_{\rm syst} \right) \times
10^{-4} ~\text{n / (kBq$\cdot$s)}$, approximately one order of magnitude below
that of commercial sources, the neutron-induced background rate, mainly from
the activation of $^{76}$Ge, is negligible compared to other background sources
in LEGEND-200.
