Veja man gpg
. Por exemplo você encontra lá:
--fetch-keys URIs
Retrieve keys located at the specified URIs. Note that different installations of GnuPG may support different protocols (HTTP, FTP, LDAP, etc.). When using HTTPS the system provided root certificates are used by this command.
Ou
--keyserver name
This option is deprecated - please use the --keyserver in 'dirmngr.conf' instead. [...]