This reference was hosted at a university called New Mexico Tech.  I've been trying to determine if this server is just offline or if it's being sunsetted.  Many google search results still point to infohost.mnt.edu or redirect to that page (not just the tkinter link).  Also, their main webpage (www.nmt.edu) also has a search that redirects results to infohost, so those links are all broken as well.

It seems to me that they just haven't stood up the new site yet or else they haven't changed their redirect, so I would assume that once they find they have broken links, they will fix this.  However, I also found an article that the creator of the tkinter docs has passed away [1].  If the infohost subdomain was his, then they might be moving all of it.

Anyway, I think we should leave the docs as they are for now with the hope they the university will fix the redirect.  If it doesn't get resolved, then we probably need to reach out to them.  Since the author is deceased, I'm not sure how it would work to try to host it somewhere else.  It would be a shame to lose this valuable reference and work.

[1] https://www.nmt.edu/news/2019/nmt_dedicates_shipman_plaque.php