what headset or bearings for trek 1.5

anyone know which headset bearings for the trek 1.5, 2009, all i know is it has a cane creek headset top bearing is a cartridge bearing mh p03m and the bottom bearing is ball bearings in a useless retainer which just corrodes, cant i replace this with a cartridge bearing same as the top one. no bike shops can say what bearings to buy, and trek are no use at all