How do you guys even search map location in game?

[MistakeNot]

Nope. Not this one.
It is not in the description nor the map. That is usually how crafting quests are. The markers are the NPC you submit the quests to, not the location you gather from.
I do notice most of the time it is mentioned in the journal description. This particular entry and a few others do not have it. Anyone who has this quest active can prove me wrong.

There might not be a usable quest marker for the quest, but "Matron's Lethe" is named on the map so you can certainly find it just by looking at the map.
Your gathering log will also list the general region where the material you are after can be found.