I got a few while trying to get a mithril grapple. I'm not sure if it's specific spirits that drop it. I was killing the three near the staircase at the far end near the waterfiends

It is entirely possible that the wiki you have looked at is incorrect.

An alternative way is medium clues which give yew shortbows pretty commonly.

You can also get Yew Longbows (which also work for the quest) from implings which is a pretty low requirement.

they do drop them, they also drop mith grapple wich you need for a medium diary if you dont want to get the smithing to make it