If you are using steel mandrel bends, you can have just about any muffler shop weld up the bends for you. Simply number and whitness mark each bend, then just sit and help the welder tack them together. Go get some lunch, and by the time you get back, he'll be done. I replaced my steel IC piping with aluminum mandrel bends, and have spent time looking for someone who can do quality high freq Mig, or Tig. If you don't know where to get the piping, check out Road Race Engineering, JC Whitney, or Burns Stainless. Automotive Engineering also typically has Hooker J and U bends in the warehouse, as well.
John