You should be able to find them locally.
You can try to loosen them when the engine is hot. Use a normal 6 point wrench or socket, no breaker bar or helper bar, if you think you're having to turn it too hard, stop. Let it cool and use some penetrating fluid, be patient and let it do it's job.
You can also use the blue tip wrench (a torch). Get the nut glowing and remove it. That usually works but not all people have a sufficient torch handy. And remember that it's hot when you get it off!
Alternatively, get some headers and convert to dual exhaust
Lawrenceville, GA