Many of the GX poisons items can be purchased from NPCs.
For almost every flower and poison kits:
Go to Morroc behind the build
/navi morocc 193/100Copied!
For Izidor flower:
You can buy these for 100,000 in Paradise Market or hunt from monsters.
You can also craft these in Veins.
Go to GX building in Veins.
/navi veins 254/255Copied!
Go downstairs to the bar.
Talk to NPC next to the bar
/navi job3_guil01 91/92Copied!
He will convert Animal Gore, Bitter Herb, Deadly Noxious Herb, Frozen Rose, Illusion Flower, and Aloe for one Izidor flower.
Sources:
http://www.inven.co.kr/board/ro/1957/1735