p0420 - CAT for CA emission

[nissan 01]

so i need a new CAT...the code came on and i was hoping it was the rear o2 sensor...i changed it and it came back in a week or so after putting 1000 miles on it. So i know they make the CAT off the manifold for non CA emissions...im from CA so i need one that is CA legal....has anyone found any for California? or only dealership? dealer is asking $692 for parts + shipping. im guessing a muffler shop will be maybe a little cheaper.

i was thinking of moving the CAT more downstream so i can use universal CAT and then just getting 02 sensor extensions to make it work. let me know if anyone has found cheaper way to buy the CAT.