I can only speak for the human town Einhoren - but if you enter the city through the main gate - it's on your lefthand side, located near the NPC's for weapon/armour and shield forging (and next to the level refinement NPC).

Please keep in mind that your weapon can break upon failure at every try. Therefore you can use preservation stones (IM or player shops), up to items lvl 70. There are no preservation stones for sale after lvl 70, with exception of a very limited amount (steep prices!) that come with the VIP rewards.