sorry, I'm french
A good muffler shop is usily equiped with a pipe bender and form what ever shape they want, either whit a cramp bender that change the shape of the pipe and give you some restriction or a Mandrel bender that keep the shape of the pipe and the diameter, no restriction what so ever. The faster you dispose of the exhaust gas the more fresh air and fuel you put in the more power you have.
If you really need a catalitic converter, by a high flow unit normally in stainless steel
check on ebay, I don't know any price range because here in montreal we don't have any emission test or regulation. so when it's dead it's out
For the muffler itself you have different compagnie flowmaster, magnaflow, trush, moroso...just a visit to a hot rod shop or a speed shop and you find everything
and you can find everything on the net
If you have time and a mig welder you can buy from the above compagnie mandrel tube lenght that you cut and weld to have the exact shape you need from front to rear.
what ever way you choose you can have a product of the same quality of the bolt on parts for half the price
and please don't say that americans or ignorant, I have family and friends that live in oncle sam's country
thank you
Denis