Mending books? How to get them?

I’ve been AFK fish farming for over 2 days now, and I’ve just been trying to look for a mending book, but alas with no luck. I already have 6 chests full of enchanted books and tools, and I’ve been fishing using a maxed out fishing rod, but i can’t seem to find one.

I’ve seen some people who’ve gotten like 3-8 mending books while AFK fish farming in a few hours, but i haven’t gotten any. I’m starting to think maybe the reason why is because i play on Bedrock edition? I’m not sure, and i need help with this. Even one mending book is ok, i just need to put the enchantment on my elytra because it breaks way too fast.