Expanding on Row's answer, I'll say that if you cannot find a mage to teach you in-game (and there is, in fact, an entire Tower full of mages who teach people in Hempstead), and you absolutely have to invent an NPC, consult with a gamemaster on IRC or through the forums first.
It wouldn't be any use to you to write a number of CDT entries in support of the second class only to have your class request denied due to problems with the NPC.
Again, however, I recommend that Castor should check out the Tower Academy in Port Hempstead.
Edit: Also, moving this to the appropriate forum.