Corrupted Windblossom

Cleansing one of these will make it into a Cleansed Windblossom which you can loot to receive Windblossom Berries.

This quest is no longer in game as far as I can see.

The zone of Felwood has a series of repeatable quests that begin with the quests Cleansing Felwood and at least one of the follow up repeatable turn in quests (for the salve):
Salve via Skinning, Salve via Disenchanting, Salve via hunting, Salve via Mining, and Salve via Gathering.

Once you have some Cenarion Plant Salve you can do the quests:
Corrupted Songflower which leads to Cleansed Songflower which gives Songflower Serenade
Corrupted Night Dragon which leads to Cleansed Night Dragon which gives Night Dragon's Breath
Corrupted Whipper Root which leads to Cleansed Whipper Root which gives you Whipper Root Tuber
Corrupted WIndblossom which leads to Cleansed Windblossom which gives Windblossom Berries

It is worth mentioning that when cleansed the plants will stay that way for something like 2 hours. Their quests can only be completed like every 10-15 minutes though.
This means you can get these buffs/items pretty consistently for 16 levels (the starter quest can be accepted at level 48, and the buffs continue to give the buff through 63) as long as you aren't dying very frequently and you actually do enough quests in felwood to keep your cenarion salve in stock (don't throw away any corrupted soul shards)

A lot of other Vanilla unique buffs seem to be unavailable after 63 as well ( Fengus' Ferocity , Mol'dar's Moxie , Rallying Cry of the Dragonslayer, Slip'kik's Savvy, and Spirit of Zandalar), seems that's when they want you to give up on azeroth buffs.