To the Op, getting SI's, and magazines in general, signed is still very much a thing. As someone who has collected signed Sport Magazines for 30yrs, i can say its a lot of fun and challenging.
My father and i started our collection together. We chose Sport, rather than SI as we preferred Sport Magazine's cover and inside photos. Plus there are only 12 per year.
Many more people seem to collect SI at this point.
One of the few SIs that i have is this one.
This is a link to my Sport Magazine collection.
https://flic.kr/s/aHsm2aCX3d
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