Martin Gardener was a great recreational mathematics expert and his column "Mathematical Games" is an all time hit. But is there any archive available online consisting of his articles (preferably in PDF format)? I searched online but I got only one or two articles in PDF format.
About 20 of Martin Gardner's books are available. In print, in iBooks, in Kindle, and probably other sources. Is there some reason you cannot pay for them?
All the "Mathematical Games" columns from Scientific American: you can get them on one CD ...about $51 from Amazon.com, cheaper from the MAA if you are a member.
Not strictly an archive, but some related materials to Martin Gardner and his history can be found at https://www.gathering4gardner.org/
Try here: https://z-lib.org/
In this site, just by typing 'Martin Gardner', you'll find almost all the books and papers written by Gardner, in particular, all the 'Mathematical Games' articles published in 'Scientific American'.