The ESC Handbooks, Yearbooks and membership lists for 1929-1939 are now available to members on the website (Resources | Yearbooks | page 2). They are mainly of historical interest, but there are very interesting nuggets in some of them (1929 includes a list of recommended outings from Sils and Maloja, and in 1936 you'll see some political issues which made it difficult for the Club to operate).
You can browse each year by clicking on its cover page - this will take you to the list of pdfs which you can view or download. The pdfs have been text-recognised, so (subject to your pdf viewer) you can search for text or copy text within them. But we haven't included them in the main search facility as this could throw up spurious results.
Thanks to Archivist John Barnard for putting this together, and to Andrew Kydd for sitting in the Alpine Club library and doing the scanning!