You may find them in the Bazaar. I had a quest for Celestia and I checked the Bazaar and it had everything I needed (except one which was a little rare) But I bought them all, and the Nettle Root if I remember correctly cost a little around 1000 coins. Good luck finding it!
Anthony GhostHunter, level 54 Grandmaster Theurgist
I cannot seem to find nettle root anywhere in KT and I've defeated at least 100 charmed slaves. Golden squash, however, was just dropped by my prickly bear cactus. ;)