The last time I saw Onion gear drop was late 2019. I wrote about it here: Onion Doublet Still Obtainable in 4.0+?. I finished my Onion set in May 2019 and even got a couple of duplicate pieces. Later that year, I got a couple of pieces on another account. That's the last time I've seen any pieces drop, and I do around 20-60 quick ventures a day.

I have a hunch that they are no longer obtainable based on the 5.4 Patch Notes, which states: "Certain items previously obtainable via retainer ventures have been removed." It looks like the way quick ventures work now is, if your retainer gear is good enough to get a rare item, then they will bring back a venture coffer. When you open a venture coffer, you get one of the items from the coffer's loot pool, which is almost always dye or retainer fantasia.

As for the Peregrine Helm, I'm convinced it's not obtainable post-1.0. I've never seen it, but I'm still holding onto hope despite 5.4's change to quick ventures.