Beble's ship can only be accessed once a day; if you buy everything he has he can only sell you potions. Beble's ship is a great place to get cheap treasure and rare ship parts (depending on the day). Go to his ship. Buy everything he has. Save the game. Turn off the DS. Turn it back on and change the system date. Turn off the DS and resume the game. You should start at your save point. Go to Beble's ship, which should be close. He should have more or new stock.