As of Wuthering Waves Version 1.1, characters who are using Pavo Plum Route & Farming Guide as Ascension materials are Changli. You can find this ascension mat in various locations in Luminous Shore, Mt. Firmament.
All 75 Pavo Plum in Wuthering Waves
You can find the first 60 Pavo Plum in the marked location above. One flower can be plucked four times so you see why there are only 15 flowers on the open-world. In addition, most of them are placed near together so just use Sensor to highlight all the nearby resources that can be farmed. And of course, you can also refer to the video on top for the location of each flower.
For the last 15, you can buy it from Koko in Shifang Pharmacy, Jinzhou. You'll need a total of 45,000 Shell Credits to buy all of them.