No universal converters are legal in California for California certified emission vehicles. You will probably find it hard to locate any aftermarket direct-fit converters that are legal in California and will need to replace with a genuine Nissan part. In order for an aftermarket converter to be legal in California, it needs to be "CARB" certified and will state that it is so. Used catalytic converters cannot be legally sold in the US unless they are tested and emissions certified. If you choose to buy one from Nissan, I get pretty good prices and service from Mile Barney Nissan. This is their web site:
www.1stAAANissanParts.com