where does a 51 carpenter find skill booksFollow

Just earned level 51 as a carpenter. Where do I find this tier of recipe books?

And when you reach 60, your books will be available from Penny Dreadful located in Barren Sky. You can reach the islands (and Penny) by taking the spires from T-Steppes or Nek Forest. She is near the zone in with no combat between her and the zone line.