NIIF Institute runs GPG key server on host keys.niif.hu. Its content is synchronized to international network of key servers.
Keys.niif.hu is member of the set of continously monitored key servers called HKP pool. If you do not insist on a particular server you might consider to configure "pool.sks-keyservers.net" or similar in your gpg.conf file. In this case your HPK client always reaches a working and very up to date key store.