Well, I'm so used to Ravelry now that if a pattern isn't on the site I feel helpless.
However, here are a few suggestions that you have probably already tried, but maybe they will somehow spark a new search idea for you:
Theknittinggarden.com sells her pattern books and they have a little photo of each pattern in the book. Very helpful, but it may not go back far enough for you.
How did you come to learn about this pattern? Can you post a pic of it or describe how learned about it? If yes, them maybe you could join the Louisa Harding group on Ravelry. Norah Gaughan is really active on the group dedicated to her knits and I bet Louisa is too. If you can describe it well, someone in that group should know about it.
Have you tried contacting her company through her Facebook page? I would say email her site but it seems to be down right now.
I know you have already checked Ravelry but I'm posting a link of Louisa scarves for you to peruse one last time before you give up.