The best place to get them is Gusgen Mines, which is west of the Teleport-Dem Crag in Konstat Highlands. The top section of the mines is the only location of Ghouls there, if you go further in the mines you will run into level 30+ mobs. Be aware that the mines are 80% undead/15% arcana (bombs, evil weapons, etc), and 5% other (slimes, worms, flies, funguars).
There are also several high level NMs on the top floor, so if you hear a siren go off inside the mine avoid the side rooms with the water pools at the end of the path.
Edited, Jul 13th 2011 2:28pm by Shaowstrike
____________________________Shaowstrike (Retired - FFXI)
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Cooking/Fishing 100 "We don't just borrow words; on occasion, English has pursued other languages down alleyways to beat them unconscious and rifle their pockets for new vocabulary."
— James D. Nicoll