Of course, in order to create a dualsword weapon you need to have something to work with, a pair of swords.
In addition to that, no Artisan would work for free. They need to make their living after all... Running the forge isn't cheap either...
Hm... There's something else... You need both swords to be well balanced otherwise you they make a good dualsword weapon. That's why you can only join swords of the same grade.
I can only work with up to C-garde weapons. If you want something better you should go to a bigger city. You should also keep in mind that any weapon modifications will be lost in the fusion.
There's more... If a weapon has some unique property it won't work. Fusion's impossible. Any questions? Of course, you know everything there is to know.
Well, choose the swords you want to get!