I have not seen a dye trader in Pre-Searing at all, but there is one in Ascalon (Post-Searing).
Oh, and it may have been my luck, but I always managed to get a lot of Vials of Dye from the Aloe Seeds just outside the gate of pre-searing Ascalon. But back then I didn't know they are worth a lot of money, so I fiddled around with them...