Indexes for the magazines used to be available printed on paper for a nominal sum plus SAE from the publishers – references in the online ME index to indexes appear to be exclusively to announcements of their availability, not an index as an article in the magazine. The online index at **LINK** suggests that indexes exist for many years from volume 4 onwards.
Bound volumes usually, but not always have the printed indexes included – that is what they were produced for so the easiest way is to find a bound volume and look for the index in there. Some ME clubs have complete sets of bound volumes.
My local library used to be able to get loan volumes from the Library for Science and Technology at Boston Spa in the UK, but I don't know if this even exists anymore. A local university might be another option.