Use https links on https://www.torproject.org/docs/verifying-signatures.html.en
The page https://www.torproject.org/docs/verifying-signatures.html.en uses three http links to servers which all support https.
These links all work:
https://gpgtools.org/
https://www.gpg4win.org/download.html
https://www.gnupg.org/documentation/
issue