Artisan Leatherworker is the person that caps your leatherworking to 225 and sells you patterns until then... after that, it's time to find a Master Leatherworker. You said good, so I assume Alliance...
Not sure where it is for Alliance honestly, as I play Horde. The Horde Master Leatherworker is in some remote village out in the jungle. Your Master Leatherworker may be in some remote village too.