Likelihood is if you're an average ADK player and looking to make some pretty cool gear, you're going to need some mending books. Unlike most servers, we here in ADK don't have villagers to make mending worthless, but instead have several alternatives!
Here are all the different ways one can get mending on the server:
Probably the most reliable method of obtaining mending books, voting for the server will give you the keys you need to open our free crate at spawn! With every attempt at the crate, you have a 1.5-3.0% chance (depending on how charitable Matt is at that time) to get a book, just for helping the server out!
McMMO continues to be a useful plugin on the server, and has a couple of skills that can help out players in their acquisition of any mending they may need!
The first way of getting mending would be the relaxing, yet also grindy and long, fishing method. Within fishing there is the skill titled Treasure Hunter, and it has several ranks, all of them with the possibility of getting a "mythic" drop, which has a chance to be a mending book! From ranks 1-5 it's a chance of .01 percent, rank 6 a .05 chance, rank 7 a .10 percent chance, up to .25 percent chance at rank 8. It'll be a long grind, and low odds still, but if you're up for it, go for it!
The second way is probably the most unreliable method, though if you're a gambling man, you can try your luck! The salvage skill is the child skill of fishing and repair, which basically means (Fishing Level + Repair Level)/2 = Salvage Level. You'll want to get your salvage up to 100 for optimal results, although the chances of it happening are still pretty low. Once you have salvage up a bit, simply take a piece of gear with mending on it and click on a gold block, and with any luck you'll have a brand new mending book!
This works on any mending gear you get your hands on that you don't need, like golden armor from bastions, or any equipment found during the monthly end-resets!
Not the most exciting way to get your mending books, but still reliable nonetheless: money. 90% of the ADK market is determined by mending books changing hands, so if you're in need, the auction house is almost always selling them! Be warned though, as mending is usually a rare commodity, it'll be going for high prices. However, if you're in need of money, remember to check out the money-making guide for any tips and tricks, and good luck in getting yourself fully geared up!