Has nothing to do with the county, really - thank the Federal EPA for their rules:
https://www3.epa.gov/otaq/cert/factshts/catcvrts.pdf
See Section 5 on Page 3 - unless you can have the efficiency of the converter tested and confirmed, it's a violation of the Clean Air Act (not just for coal fired power plants anymore, Toto). It also makes the salvage yard liable for a violation if they were to sell it.
Unfortunately, that means you either are stuck with the OEM, or see if you can find a aftermarket that will fit in it's place - Magnaflow makes some small units that a skilled welder could probably fit in there...