Maybe it would be possible to scrape the ISBN's and get them from Library Genesis?
You could have done that at any time in the past few years tho.
Why? I can understand downloading a few that look interesting, or asking for permission to mirror them, but blindly downloading all of them seems like hoarding.
Seems like? No, it is hoarding. :)
Call it "creating a local cache in case the service goes down" (and it most definitely will). "Hoarding" is the normal thing you do when dealing with digital stuff.
And...they are no longer available. Hope someone saved them.