There're tons of knives sold at any weapons shop.
You have your Throwing Knives. You can get all sizes for hiding them on your body. Depending on your aim, these knives are better at long range, not up close, although a stab to the back is just as effective. I don't know how things are where you come from stranger but a knife in the back is a normal way of dealing with someone here in Nemus Rad'n. Watch yer back stranger. That's not a threat, that's good advice.
Fighting Knives are a good deal larger, made for close range battles. You should carry at least two so you can block the sword and still be able to fight.
Sword Breakers are also used. We got some nice ones here. These ones here are 'specially made for peacekeeper blades. Not to say you'll ever use em for that of course.