Most salvage yards won't even sell converters- either legal issues, or they're just worth more as precious metals...

if you can't get a "universal" cat to fit (many post- y2k vehicles will be so designed) then your cheapest bet is to move to the country where they don't bother with things so trivial as emissions testing... :-)

more seriously, tho- what's wrong with it? if it's rattling- then yeah, you need a new one, and maybe a new muffler, as pieces of it may have clogged it up...

is it clogged?

or what diagnostic codes from the computer?

before you even ask- yes, I have "trust issues" with all mechanics... not all of them are crooked, some are just taking the easy way out, or actually believe there's no alternative to replacing it.