Ask a Warrior Thread.

A skill has to be at level 15 before you can use the Mastery 30 book. Hence, you must use the 20 first.

Mastery books don't drop from monsters anymore. Mystery Mastery books might, but the chance of getting the book you need from one of them is miniscule (there are, what, 500 different 4th job skills in the game now? more?), *and* those books can fail.

I tend to get unlucky with item chances, darn lol.

I'm afraid those were removed some time ago. Specific mastery books were replaced by Mystery Mastery Books quite a while ago, somewhere pre-Justice/Renegades, and I think those books are replaced too, although I'm not sure. The only option now is either to find old books on mules, which should still work, or buy the Mastery Book 20/30s. Also, you need to use 20 before you can use 30.
I personally don't play in Scania, but maybe somebody who does can help with the books?

One last thing: Nexon replaced the normal AP resets with full AP resets in the Cash Shop some time ago. While I don't know how expensive they are, they might be a decent option because I seriously doubt there will be anymore full AP resets coming this long after Tempest.

Yeah all I see is a single AP Reset.