macro to retreive openpgp certificate?

[ilf]

Sometimes I view mails with an OpenPGP signature without having the 
corresponding certificate, then I get the error:

> Can't verify due to a missing key or certificate

Does anyone have a good macro to retrieve that specific OpenPGP 
certificate and re-check the signature?

Something along the lines of "^K" "extract-keys" "extract supported 
public keys".

-- 
ilf

If you upload your address book to "the cloud", I don't want to be in it.