The epa-search-keys command can be used to query a
GPG key server. Emacs will then pop up a buffer that lists
the matches, and you can then fetch (and add) keys to your personal
key ring.
In the key search buffer, you can use the f command to mark keys for fetching, and then x to fetch the keys (and incorporate them into your key ring).
The epa-keyserver variable says which server to query.