On my diesel, when I had the catalyst removed, I took to a specialist exhaust place.
They cut out the cat and welded in a section of automotive grade stainless steel pipe between the headers and the resonator.
They did excellent work (job was done almost 5 years ago) and never had a problem. Looks factory original, unless you really know what you're looking for.
You will most likely have to go a similar route by finding a good shop through Google, yellow pages, yelp, etc.