First of all, save a copy of your save game, then put this one in the save game folder, all the weapons are avaliable to use, the only one out of the game is Crescent Axe, you can buy it from Patches in Firelink Shrine, the save file contains another caracters, the one ready to unlock the achievement is "Geralt" a poor Witcher cosplay hehehehehe just load and go find patches.
I'm not responsable for any trouble caused by you, so be sure what you doing before moving files.

Most of the weapons are quite simple to drop, but Channeler's trident stole all my patience, so i used a well know trick to unlock all wepons but the Crescent Axe, your steam must be online to work.
Removed itens are not included to avoid problems, but after this save i picked all of them in my save file without any worries.

Praise the sun guys  ...     Y