Yes I'd my recommendation would be to download a garrison mod and peek at the files in PFM to see what they did and then make your own custom changes to the relevant MOSS db file (ie whichever one governs the building_armed_citizen_junctions table).

MOSS probably conflicts with those mods because they have overlapping unique IDs for the new garrison units so you could also try changing those numbers in the other mod and see if that allows it to be paired with MOSS (but that also might not work since MOSS uses a lot of custom units).