How to find forks of a deleted github repository? 

method1:

This search query on Google may help:

"forked from {user-name}/{repo-name}" site:github.com

for example:

"forked from jiix/xiunobbs" site:github.com

method 2: GitHub search commit by hash

https://github.com/search?q=bcbc5dc54055d14996b256d348fb75cc6debe282&type=commits 

method 3: Internet Archive

https://web.archive.org/web/20220611112942/https://github.com/jiix/xiunobbs

https://web.archive.org/web/20220611113016/https://github.com/jiix/xiunobbs/network/members

It's probably not in it, but there you can easily click the links to check it on archive.org and smaller archive sites.

https://cachedview.com/

https://archive.is/

https://archive.softwareheritage.org/browse/search/

reference

https://gist.github.com/rjeczalik/81ff08b59d7841970fca82ca39f40a10

https://trufflesecurity.com/blog/anyone-can-access-deleted-and-private-repo-data-github