Many thanks to Paul Evans (W4/VP9KF) who writes:
If you’re using a logging program and you need instant look-up of who is in what CW Club, you can use the following page, which I look after:
CW Club Call History files: http://www.g4bki.com/club_call_history.htm
These files are kept up-to-date on a daily basis. You’ll see that this currently lists memberships of 69 different clubs, including the vast majority of QRP clubs, a surprisingly high number.
One exception: G-QRP [who] told various sites that used their (previously open) membership list to cease using it.
Thank you, Paul!