1 to minimum frenzy charge

Hello, is that specific drop from syndicate member or its just totaly random ?

According to Wikia, it's a random unveil. No need to farm specific members. It can only yield in Rings and Amulets.

On a side-related note, Redeemer's Shields have a small chance to have a +(1-2) to Minimum Frenzy Charges, depending on their ILvl

Please remember that Minimum charges will not be consumed/spent by skills, thus they cannot be used to bypass cooldown limits from skills (For example, Flicker Strike)

its jewelry from any member, if you trying to get it unveiled best bet is aisling for extra veiled items, if you get a ring/neck with +1 frenzy you can also get the same unveil by removing the crafted mod then adding it back on with aisling on research, the unveil options will be identical to the first time so you can use 1 item to repeatedly unlock the same veil.