According to Andrew from SilencerCo, the Y-mounts will be released late March or early April. So, no one has one because they do not exist yet. I am also invested in YHM mounts heavily, and while I bought a 762 Saker with the Trifecta mount (as I plan on switching over eventually) I will be buying a Y-Mount when available. The one part that really sucks is I was told $295 MSRP on the Y-Mount, which seems really high if it is basically just a thread mount with a larger hole and some serrations on the back, so I hope it has something great to offer that hasn't occured to me.
If I didn't have a permanently-attached YHM on my one barrel and an issuew with handguard interference with a Trifecta/Saker on my other, I'd have gone right over to the Trifecta.