So I was planning to craft some poisons as I managed to get high enough survival skill. Problem is all the three default poisons in recipe list (bleak venom, mother darkness, tremble) seem to use 3x bark scorpion poison glands x3 and I am struggling with stacking those atm. I know few locations where I can surely find a Bark Scorpion or two, but even so they mostly don't have those glands when attempting to loot.

Anyone found a good spot with loads of Bark Scorpions, or is there any vendor around selling poisons or poison materials?

White Horsenettle and Cazador Poison Glands are easy to come by, still struggling with killing Cazadors though

hidden valley and small cave type thing north eastish of nipton seem to have decent sized groups of them.

Also, are poisons for melee use only? how exactly do they work?

Apparently they are melee only. Once you manage to craft a certain poison it shows in items/aid in pib-boy. If you click (try to use) the poison it says "you must first equip a weapon that can be poisoned". So yes you have to have a melee weapon equipped to poison it....bit shame as I was hoping to be able to poison bullets

Scorpion valley east or south east of hidden valley. Lots of bark's there but 4-6 giant rads too.