Two personalities of the same person slugging it out in an alley and you wanta know where the swords would have come from? Have you ever heard of a thing called the "willing suspension of disbelief?" And for that matter, it wouldn't have had to necessarily been swords. Spike and Angel used pieces of rebar when they were fighting over the Cup of Eternal Torment, and Angel and the Brothers used sections of an iron fence when they were fighting that Aztec demon.
As far as that goes, weapons weren't the point anyhow. There just wasn't enough...maybe what I'm looking for is, like the immortal Bruce Lee said..."emotional content, NOT ANGER!" This is a fight that had been building up for the better part of two centuries, and it looked like any other Buffy/Angel brawl.
Look at the fight between Buffy and Spike when he had the Gem of Amara, or for that matter, their fight in "School Hard." Bangel and Spuffy aside for the moment, those fights and just about every other fight Sarah and James had, had style and class, probably the best in the whole series. I don't know if they were trying to portray David as having a different fighting style or if the stunt choreographer was out with the flu when Angel fought Angelus, but the fire just wasn't there.