where do i get the lost trader quest?

here you go. LostTraderQuest (http://www.gamebanshee.com/fable/walkthrough/losttrader.php)

walk into the cave next to the hobbe cave.
then a trader will show up and ask u to find his Bro.
just walk and slay all bandits in the way and you'll meet him not so far away from the entrance.