Jegs, Summit, your local exhaust shop... all carry stainless pipe, but the exhaust shop can expand the ends of the pipe for you to just slip over and band clamp in place.
Save the cats and leave them intact, you never know when your state might decide to change the law, you may move to another state, etc... There may come a time you need them.
What about inspection thought la was a mother f er on that stuff get caught with no cats thats a big fine. And you got high flow cats removing them will net you not that big of a difference.
Here in LA they don't drive, get in or even look under the hood. Just pull up pay your $20 every two years. But im just going to keep then on, they really aint hurting my performance.