Prontera, at the right side of the fountain theres a few houses with armor and weapon shops, in payon a bit down of where you get when you go into the map. Damascus is one of the best/cheaper daggers, but the one in shop have only 1 slot, you can find 2 slotted ones from players, if you get the money to buy them.
Also, if you don't know about this already, you can search player shops here pc.bot.nu
Katars are cheaper but I personally don't like them, less slots and not as much damage as my 2 damascus