Information about drop rate and other crafting materials you can find here.
Death's Breath can be obtained by killing elites.
Therefore we need a spot with a fast and easy killable elite at the highest difficulty level.
1. Start Campaign Mode Act 1 - Quest 6.2 Speak with Alaric - at normal difficult
2. Go into Festering Woods
3. Search for "Warriors Rest"
4. Teleport to town and leave game
Now start game again at higher difficulty.
I suggest a minimum of Torment I, also with bad starting gear.
You can optimize your skills only for this one elite pack.
1. Take TP to Warriors Rest
2. Kill elite pack with optimized skills.
3. Pick up all items.
4. Teleport to town.
5. Leave game and repeat.
Optimized Skillset for Barbarian with starting gear
L - Frenzy - Maniac
If you have surviving problems you can use smite for stun.
R - Avalanche - Tetonic Rift
If you have surviving problems you can use Glacier for freeze.
1 - Leap - Death from Above
To Jump into the elite pack.
2 - Wrath of the Berserker - Insanity
damage and immun to imparing effects
3 - Earthquake - Molten Fury
4 - Warcry - Invigorate
for better survival
P2 - Weapons Master
P3 - Berserker Rage
P4 - Superstition
There are many useful skills. You can experiment by yourself what fits you best.
Warcry and run until I see elite pack.
Jump into elite pack.
Activate Wrath of the Berserker.
Frenzy to full fury.
Use Jump again.
Use Avalanche and Earthquake.
Then use Jump if I must escape or need a stun to survive.
Finish elite pack with frenzy.