Duskwood, just run along the northern coast and kill all the blue spiders you see. They start to appear on the coast just north of the graveyard filled with zombies, and the whole coast is filled with them all the way to where duskwood zone changes to another in the east.
Just out of curiosity, why farm these? Don't they cost like 1g each on AH (not 100% sure about this though) and what do you use it for? Spidersilk Boots?