> The one that's supposed to be at <http://schemecookbook.org/> has
> apparently vanished from the internet.

Hooray, good old Wayback Machine has copies :)

Latest one is from 2015. Table of contents:
<http://web.archive.org/web/20150206034904/http://schemecookbook.org/Cookbook/TOC>

It's published under LGPL:
<http://web.archive.org/web/20150208033030/http://schemecookbook.org/Cookbook/BookIntroduction#Contributor_Agreement>

Let's make a copy under the Schemedoc organization and modernize it!
Would wget mirroring work?