This is a useful technique I read about a while back in my PSM magazine when FF Tactics made its first debut.
I found the magazine in my archives.
Now I am going to share it with you all, no need to thank me.
To begin with, open up the menu screen. Then choose a character that has the "Two Sword" ability. Choose the desired weapon you wish to duplicate.
Equip the weapon on to that character's left hand,( it is imperative that you do this. )and a shield on to the right hand( you must have a character with the appropriate job qualifications to equip a shield ).
Now, go to an item shop, in any city, it doesn't make a difference which one. Select the character specified above to enter the "Fitting room", and select the option "Best fit".
Then you simply select " Quit fitting", for your left hand, then exit the fitting room screen, and once you have left the store, you should have an exact duplicate the weapon equiped in the characters left hand.
NOTE: You still have to pay some dough out to do this. But guess what? The Excalibur only costs 10 gil! What a deal.
I have only tried this with swords, but it could work with knives and axes, I don't know, try it. I would try it myself, but I no longer own this game.