You can either buy bend pieces (I think Summit Racing sells them or some other car speed parts site) or design your pieces and have it done by a larger muffler shop.

It's a little harder to find stainless bend pieces.

 

The best method would be to utilize stainless and a tig welder for exposed exhaust work. I have ordered from Burns in the past when doing turbo exhaust and intercooler piping that needed to be rust free and decent looking:

http://www.burnsstainless.com/