Seriously, It's kinda strange logic.

Items were usually pokemon based, no?

Why Pikachu in Viridian forest can have Light Ball, while all Pikachu's at Power Plant have only Oran Berries?

Same goes to Snorlax

Why Snorlax at Route 11 can have Leftovers (btw, this one is member only), while Snorlax at Route 12 doesn't have em?

It is done this way in order to increase the rarity of certain items, and also to allow a variety in spawns, so that it is not the same to hunt a specific Pokemon in every map, but instead you have to go to a particular map if you want said Pokemon to hold an item.

105887 It is done this way in order to increase the rarity of certain items, and also to allow a variety in spawns, so that it is not the same to hunt a specific Pokemon in every map, but instead you have to go to a particular map if you want said Pokemon to hold an item.

 

Yet, there is not a single guide that specifies locations of those.

I cleared like 6 areas just to see if it's true that Vulpix can hold Charcoal, and all i got was berry.

105909

105887 It is done this way in order to increase the rarity of certain items, and also to allow a variety in spawns, so that it is not the same to hunt a specific Pokemon in every map, but instead you have to go to a particular map if you want said Pokemon to hold an item.

 

Yet, there is not a single guide that specifies locations of those.

I cleared like 6 areas just to see if it's true that Vulpix can hold Charcoal, and all i got was berry.

 

Guide-making is not a staff obligation, but any user is free to create the guides they deem useful. As you said, there is currently no complete guides about held items.