... the three swords are Special... They were made to counter the influence of 30 Fallen Angels that are partly free from Hell . If you're looking for "This guy was picked by God to fight evil" there's an entire section of powers in the book dealing with Faith. It's just that only three of them get Swords.
I'd say rather that Only the Knights of the Cross are chosen to wield those particular swords. As Bujin said:
The mythology of the Knights of the Cross is specifically tied to the three nails that Jesus was crucified with, pitted against foes representing the Judas' 30 pieces of silver.
So, while I wouldn't alter anything regarding those swords or their wielders, I do believe that there is room in the Dresdenverse and certianly room in your game if you so desire for other holy or magic swords and their weilders. Literature is full of examples, St. Joan being only one of them.
In my campaign, the players have recently uncovered information about an unknown branch of the Order of Santiago which was not secularized in the sixteenth century, but instead continues to watch over four Swords of the Saints: Joyeuse, Durandal, Curtana and Almace, and their potential wielders. [Note: I chose these with reference to the Song of Roland and each contains relics of a specific patron saint.]
Of course, Charlemagne’s sword is said to have been buried with him, and Curtana is currently in Ultima Thule…