Editing shops is hard and you need to edit both client (of every player on the server) and server files. You can buy the normal 2nd class job skills in Luna (/go 4), the rest of the skills you can usually find from candle ghosts in most servers.
I was seeing in one another site that in the truth who has that to sell skill of the second Job in the truth it is the Darren in Junon Polis, it will be that they nobody has the archive to adjust this?