It is still a thing. I have over 200 plus signed issues (baseball only). I agree the older issues are some of the best covers. I also agree that SI is holding on by a thread and the stars on the covers will be expensive to land. An extra Fisk auto ticket at a 90's Tuff-Stuff show led me down the signed SI cover rabbit hole. A dealer had the 1972 Fisk cover, which I thought was cool and better than the standard stock 8x10 photo. Ebay also helped in providing a way to purchase the older magazines. No label magazines or covers were the label was removed are ideal but I have magazines with labels as well.
The King:
http://sikingcollection.com/
Another great site:
http://www.sicollection.com/index.html