According to npm
https://www.npmjs.com/package/mongodb-core it's there. However that said.
NPM is using master-master replicated couchDB instances so it might not have replicated to your geo local one.
you can see if NPM sees it by doing
npm info mongodb-core
I would just try again it's likely that it's made it's way over to whatever region you are. They get published in the EU region.