All the vanilla tools are in the loot table, it'd make sense to have knives there too (enchanted)

This has already been implemented, a while ago:
https://github.com/vectorwing/FarmersDelight/blob/1.20/src/main/resources/data/farmersdelight/loot_tables/chests/fd_ruined_portal.json

Try going into a Creative world and opening a few ruined portal chests, and a knife should eventually show up.