#1 Leather is Tailoring...Armorer allows chain and plate and the appropriate shields for that armor class.
#2 The armorer essentials can be purchased from the merchant, but the advanced armorer (with all the desired recip's for the desired armor) need to be purchased off the broker or found as drops from the appropriate lvl MOB.
For example if you're looking for advanced armorer lvl22 you should be killing lvl 22 mobs. That's been my experience, and I've read that a few times in other threads, but it might not be true.
Buy them off the broker, it's really the fastest way to get all the advanced books. BTW you will be able to find advanced outfitter books as well, which have some nice items (you're past them now though) that can be made with Blackened Iron.
Edit in Bold
Edited, Sep 8th 2006 at 3:07pm EDT by Volstrum
second edit cause I'm careless
Edited, Sep 8th 2006 at 3:14pm EDT by Volstrum
Edited, Sep 8th 2006 at 3:12pm EDT by Volstrum