Kind of surprised there’s no mention of Fletchers’ Mill [0] here, they’re good quality mills made in Maine. The pepper mills use stainless steel while the salt mills use nylon (corrosion resistance), so you’d have to look elsewhere for salt.

Personally I just dump kosher salt into a salt cellar and call it a day but I am sure there are plastic-free salt mills out there somewhere.

0: https://fletchersmill.com