What is the best villager to get emeralds from?

I am grinding emeralds to save up for some mending books from a librarian villager. However, it costs 38 emeralds (the most expensive price for an enchanted book), and I am having trouble getting emeralds to save up for them (~10 minutes per emerald). I have several novice villagers; I just set up my villager trading hall:

• Novice Weaponsmith: Default Novice trades
• Apprentice Toolsmith: 15 Coal for 1 Emerald, 1 Emerald for Stone Axe + Default Apprentice trades
• Novice Farmer: 20 Wheat for 1 Emerald, 1 Emerald for 6 Bread
• Novice Armorer: 15 Coal for 1 Emerald, 5 Emeralds for Iron Helmet
• Novice Librarian: 24 Paper for 1 Emerald, 38 Emerald + 1 book for 1 Mending book (target)

Which villager should I farm-trade with, and if none of those are preferable, other villagers can be used as well.

Solution 1:

A Fletcher villager (with it's workplace block being the fletching table) that sells sticks for emeralds is a pretty decent and cheap trade. If you're able to make a dark oak, giant spruce, or giant jungle tree farm, or you just happen to have an over-abundance of wood, then this villager will prove to be very useful.

Solution 2:

I like to use the Apprentice/Novice Stone Mason. They offer 1 emerald for 10 clay and also 1 emerald for 20 stone. It's a grind but worth it

Solution 3:

Clerics will trade Emeralds for Gold.

If you have a gold farm, this can be an efficient way to get Emeralds.