You'll be lucky to find one to be honest mate. Most people don't want to part with a downpipe as it renders the rest of the system useless. I shall be getting my ASBO powerflow exhaust fixed this month, so it will make my janspeed system surplus, but I would only be willing to sell the downpipe for a price that'd cost the whole system.
Im definitely getting my powerflow exhaust fixed now as the janspeed back box I believe is disintegrating inside, so if you can wait til the second week in october, I'll sell you my downpipe