Cobra Scales are skinned from the following mobs:
- Cobrahide Leg Armor
- Nethercobra Leg Armor
- Stylin' Adventure Hat
- Stylin' Crimson Hat
- Stylin' Jungle Hat
- Stylin' Purple Hat
Where to learn the recipes?
Both of the above leg armors are sold by Hellfire Peninsula Quartermasters, that would be Honor Hold for alliance and Thrallmar for Horde. The hat recipes drop from some instances, specifically Sethekk Halls, Black Morass, Durnholde and Shadow Labyrinth on normal and heroic modes. They are BOP.
How much are they worth?
How much you ask for these is very much your choice. I'm sure you will be the only one selling these. I usually ask 1000-1500g for one leg enchant, as they are only needed by elitists who want to enchant their level 60 epic PVP pants with the best enchant available, dps wise.
Scales itself sell for even 400g a piece sometimes.
Stylish hats are harder to price. They are vanity items. They look cool, but are useless otherwise. Only a high level banker would need one in my opinion.