Can somebody confirm if yak milk is obtainable via retainer?

[Gunspec]

Consistent money earners should be an equally good choice.

the income is pretty decent.

I'm speaking from the perspective of someone leveling leatherworking, and it takes 15 minutes of farm to get enough skins to make a single piece for a level 50 leve that requires 9 pieces. I don't want to finance your entire housing ward just to level a single profession. And your retainers (which can be bought with real money) shouldn't be a significant source of gil income, because that is literally pay to win.

People should make bank on endgame gear, not leveling components. That is why hippogryph skin drop rates were never changed in 2.x, while aldgoat, toadskin, and boarskin were buffed substantially.