MK III exhaust
 

Hi I am doing full exhaust, headers are on and kickass. where can I find good stainless steel piping to do the rest back to the muffler?

Are you looking for just the piping or are you looking for an aftermarket Catback Exhaust? Cause if so you can find a lot of stuff from suprasport.com and suprastore.com
There are a lot more suppliers to get parts from but these are just some I have used and bought from.