These are guides and tips specific to thief class.

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.
  1. Go to GX building in Veins. /navi veins 254/255Copied!
  2. Go downstairs to the bar.
  3. Talk to NPC next to the bar /navi job3_guil01 91/92Copied!
  4. 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