How to fetch all signing keys?

Sebastian D.B. Krause
Sun Jun 2 03:42:02 2002

When I type "gpg -kvv" there are many signatures marked with "[User
id not found]". How can I say GnuPG to try to fetch all these
unknown keys from a keyserver (I've alreays set "keyserver" in the
options file)? Do I need a script (where can I find one?) or can
handle GnuPG this itself?