I work on OpenStack, which is a project folks work on primarily due to sponsorship -- not many people who want to do security/stability work for a cloud "for the fun of it" :D.

So mentees I've worked with have usually come as part of a program, such as MLH[1] or Outreachy[2]. Other projects I've helped with mentoring have come from college programs or professors[3].

I have no idea how hard it is to get through the filters to get these opportunities; I know generally we ask them to only send us the best and that's worked out really well.

[1] https://www.youtube.com/watch?v=fbsI8l-MaFA is an interview done on my podcast (by the other host, Tabatha) with CID, who works with me on OpenStack Ironic. A little over 2 years ago, he was an MLH fellow (https://fellowship.mlh.com/) working with me -- now he's a maintainer on OpenStack and working on my team. This is an exceptional outcome, but he's not the only person who has found success via MLH that I know.

[2] e.g. https://lists.openstack.org/archives/list/openstack-discuss@...

[3] https://lists.openstack.org/archives/list/openstack-discuss@...