I realise that this is a very old post but I am providing an answer in the hope that someone may find it useful.
On a Windows PC, GPG stores its keys (both public and private) in %appdata%\gnupg
(e.g. C:\Documents and Settings\myusername\Application Data\gnupg
). So, just drag the secring.gpg
file from that folder onto the window of your currently installed version of Kleopatra and select the 'Import Certificates' option.