Herb nodes are pretty scattered and the varietal versions seems even more that way. So hunting around the core Tyria area thus far I've found the following:
Varietal Peppercorn - Diessa Plateau, EotM (N.B. after nearly 2 months and lots of hours spent scouting on my thief/cook no drops at the synthesizers in regular WvW)
Varietal Mint - Fireheart Rise, Iron Marches, rarely in Bloodtide Coast south edge
Varietal Clove - Mount Maelstrom-more than you will likely need. I often get multiple harvests on each swing without a booster & frequently(1 out of 4) net 2-4 varietal cloves per swing
Varietal Cilantro - Bloodtide Coast northern half
Varietal Sesame - Bloodtide coast southern half, and The newer Path of Fire desert areas.
*Anecdata is multiple anecdotes pasted together to appear "like" actual data.
**will update as I poke around a bit.