Is there a readily available, easy to use electronic index to MM articles. I haven't found one yet. 

I didn't subscribe.  I did buy almost every issue in my LHS up until about 2001 when my mainline modeling interest waned and I went off on a narrow gauge tangent in F scale for about 6 years. by then MM was gone.
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Ken Adams
Omicron BA2.2 may come and go but I still live mostly in splendid Shelter In Place solitude
Location: About half way up Walnut Creek
Owner PlasticFreightCarBuilders@groups.io