Where do you find Rashvine in Dragon Age Inquisition?

Acquisition

Random loot from sacks.
Found in Emprise du Lion, Emerald Graves, the Exalted Plains, and in the Lost Temple of Dirthamen growing on walls, rocks and trees.
Available at the Village of Crestwood Merchant for 42 .
War table operations:
Available at the Winter Palace Merchant for 42.

Where can I buy Rashvine nettle?

Found on the Exalted Plains: One node can be found on the southwest side of Var Bellanaris, under the arch behind the Fen’Harel statue. Two nodes can be found in the Path of Flame, both are located southeast of the western entrance to the Eastern Ramparts near the Riverwatch Inquisition Camp.

Where do I find infusion primers in Dragon Age Inquisition?

Crestwood
To find the Infusion Primers, you need to travel to Crestwood and search the areas of East Side Hills, the Black Fens, and the Flats, and kill the three rivals you find. The screenshot below shows the map of the area, and the red circles indicate where you can find them.

Where do I find way of the Reaver?

Writing on Reaver methods can be found beside Iron Bull at the Skyhold tavern Herald’s Rest, adjacent to where he sits. If the Iron Bull was not recruited, the book can be purchased from the book merchant Willvan in Val Royeaux. Reading it unlocks Codex entry: Way of the Reaver.

How do I get Reaver specialization?

If he is not provoked he will offer the Warden a vial of blood to pour on Andraste’s Ashes. Once the Warden has navigated through the Gauntlet, pour the blood into the urn and speak with Kolgrim outside. He will teach you the Reaver specialization.