Does anyone the location of the serial numbers for 2004 CARB Subaru Outback Catalytic Converters?

I replaced most of my exhaust system a few years ago (catalytic converters and O2 Sensors) because of a P0420 error. My car came from a state that required the vehicles to meet strict emissions standards for the year. As a result I had 5 O2 sensors and 3 catalytic converters. Fast forward to 2021 where the prices of the metals in the cats are astronomically high, making me want to sell them. In order to do so, it is helpful to have a serial number to prove it’s an OEM part. So, for this year of Catalytic Converters, or any Subaru cat, does anyone know where it the serial number might be? I’ve taken steel wool to the bodies and heat shields and have not been able to find anything.

Part 2 is that is you know of any reputable sources to sell cats to, I’d also like to see that. Out of scope for the site.

Edit:
Left Exhaust PN: 44101AE10A

Right Exhaust PN: 44101AE08A