I am wholly unsurprised that Harold Innis (1894-1952) maintained a card index (zettelkasten) through his research life, but I am pleased to have found that his literary estate has done some work on it and published it as The Idea File of Harold Adams Innis (University of Toronto Press, 1980). The introduction seems to have some fascinating material on the form and structure as well as decisions on how they decided to present and publish it.
For those unaware of his work, primarily as a political economist, he wrote extensively on media and communication theory including the influential works Empire and Communications (1950) and The Bias of Communication (1951).
While I appreciate the published book nature of the work, it would be quite something to have it excerpted back down to index card form as a piece of material culture to purchase and play around with. Perhaps something in honor of the coming 75th anniversary of his passing?