Excelsior

Where is it then?

There is no official guide unfortunately. There are a lot of players that have completed it though, so if your stuck you can ask in world chat or on the forums for pointers.
The instructions are pretty good though, throughout the quests.

There is partial answer to your question. Some people are keeping Karate Quest guides as a in-game books.

DreamStalker has a house "Rune Library" in Malas , west of Grimswind Ruins
on World Teleporter under Shops Tabitha has those books right next to teleport ... look for table with belts.
and never, ever try to solo Red Belt

use blank book and insciption skill to copy book about your current quest.

All right guys, thx a lot!