i’ve never done it, but i would think it should be relatively easy to extract, if you have a starting point for defining the administrative places that you want boundaries for. (you would just automate the process described here, i think: https://forum.inaturalist.org/t/how-to-import-a-place-from-openstreetmap-into-inaturalist-using-overpassturbo-web-based/41046)
Wikidata could be another source for boundaries via the geoshape property, but i don’t know if that would be better than OSM from a data quality perspective.