My fund fits the criteria, but I don't know the YC partners personally...
If you go to https://demoday.ycombinator.com and try to login, it gives you an e-mail address... maybe try shooting an email to that person?
Apologies if my reply came off as glib - I'm surprised (though only through my ignorance) to learn a personal connection may not be present despite a number of mutual connections. I guess the volume of YC companies has had that effect over the years.
No worries. I think many investors know at least one YC partner, but many do not. YC is so big these days =). Last demo day was probably ~150 founders and maybe ~500 investors.