You do not need the skinning profession to salvage from a mechanical mob.
Salvaging, or mob engineering, is an innate ability that comes from taking up the engineering profession and can be performed only on mechanical mobs. It works similarly to skinning, in that, you right-click on the mob you just looted a second time for profession-specific loot (other similar loot abilities are mining on stone golem type mobs (mining) and herb-collection on bog lord type mobs (herbalism)).
The only way to loot this schematic right now (as of 4.3.4) is to farm for it yourself on mechanical mobs. They have a chance to give you the schematic when you loot or salvage them. The wowhead page you provided gives you a comprehensive list of mobs that drop this, so I am not going to repeat it here. As it is bound on pickup, you won't find it in the AH.