Project-GC uses (most of the time) OpenStreetMap as source for such things. I have looked at this before, but it didn't look complete then, or I missed something. When I took a look today, it actually looks like it might work out.
Since Groundspeak has region data, we need to find a level that matches theirs, and hope that theirs isn't out of date. We will investigate this and see where it ends.
UPDATE: Region data for Japan has been imported, it may take a few days until it works everywhere. County data isn't possible yet, since OSM isn't complete.
