Based on NPC sell orders and/or drops are some skill books only available in certain places?
serker [ Editor ]
Drug Manufacturing skill can be bought via npc sell order in null-sec only, from number of pirate corporations. Mining Director and Mining Foreman skills are being sold by Outer Ring Excavations in their stations.
Various weapon specialization skills(Amarr Drone Specialization, Cruise Missile Specialization, you name it) are being sold in the regoins that belongs to certain empires, say, missile skills are in Caldari regions, artillery/autocannon skills in Minmatar regions. Blaster spec being sold in Gallente space and railgun spec in caldari space. Drone spec are pretty straightforward, amarr spec skill in amarr regions, etc.