do you need to hunt herald lvl5 for sunder charm ?

Honestly I wouldn't think they exist if I didn't see people selling them.
T5 herald has the best chance but I have yet to get one to drop.

T5 herald on 8 player game = 2% chance or something

Here is the data mined data

Level 1 Herald:

p1–2: 0.3677% (~1 in 272)
p3–4: 0.7326% (~1 in 136.5)
p5–6: 1.0950% (~1 in 91.3)
p7–8: 1.4545% (~1 in 68.8)

Level 5 Herald (3x drop rate of Level 1):

p1–2: 1.0949% (~1 in 91.3)
p3–4: 2.1659% (~1 in 46.2)
p5–6: 3.2139% (~1 in 31.1)
p7–8: 4.2388% (~1 in 23.6)