crDroid was mentioned for ginkgo in another thread, but this seems to have changed as far as I can tell.
DivestOS seems to have at least hlte and oneplus3 (probably more, I just checked two random ones) listed as end of life but reported working with the last update 15 days ago. Not sure if that means they currently receive security updates or not.
Others here are probably more knowledgable – my point is, if someone somewhere is generously putting in the time and effort to maintain a port of their ROM for these devices, it would be good to find a process by which to share these efforts across various custom ROMs since a lot of perfectly good devices could be saved that way.