So as I could not find an answer online, I just manually searched every loot table in the game to get an answer which I have now added to the wiki.
But anyways here we go:
Treasure enchantments (Mending, Frost Walker, Curse of Binding, and Curse of Vanishing) can be obtained from the following:
- Jungle Temples (enchanted books)
- Stronghold coridor, crossing, and library (enchanted books)
- Fishing (both enchanted books and items)
- End Cities (only items, not enchanted books)
- Librarian villager trades (enchanted books)
Update: The aforementioned are chests that can roll books guaranteed to be "treasure enchantments" such as mending. However, there are a few other loot tables in the game that have "randomly enchanted" books that I was not aware apparently have a chance (small though it be) to be a treasure enchantment as well. These include:
- Dungeons
- Mineshafts
- Ancient Cities
- Desert temples
- Pillager Outposts
- Underwater ruins (big)
- Woodland Mansions