I am conducting a study on assessing integrated risk of municipalities in the world, so I need the digit boundaries. Your quick response are highly appreciated.
As far as I know, there is not a world wide database with boundaries of all municipalities. I think it will be a tough job to collect them for each country separately. For the Netherlands you will find the boundaries here (maybe in a local projection): https://www.pdok.nl/nl/producten/pdok-downloads/basis-registratie-kadaster/bestuurlijke-grenzen-actueel (this website is in Dutch, sorry for that)
Maybe there is someone out there that has done the job of collecting all boundaries already? I wish you all the best with collecting the remainder of the data...