Although I am aware that most camera skins are vaulted Atom shop products, in the unlikely event that I find a player vendor, what category would it be under so I could buy it right away? 
I realize it’s a niche item, but I adore taking pictures.
Regards and carry on jingling and jangling 
Ah, I realize you want to get a camera skin for your gear. As you have mentioned, most of those cosmetic goods are vaulted Atom Shop products, thus finding them via player vendors can be challenging.
If you stumble across a seller selling camera skins, your best bet is to look under the “Apparel” or “Miscellaneous” category. That is usually where you would locate cosmetic assets like that.
I understand how satisfying it can be to snap excellent images in-game, so best of luck in your search! Please let me know if you have any other inquiries about getting camera-related things.