sorry cant help you there
but if you get some ally ones and you want them shiny i just got some stuff from the states its the best stuff i have ever used
can only use it on raw ally but a few wipes with this stuff and it comes up like chrome
some bits might need more work then other but did my abs pump today once i got it and was only like 10 rubs and it was shiny
stuff is called blingmaster think the only one that sends to the uk is guy http://www.detailsupplyonline.com/product_info.php?cPath=73&products_id=120
i went to a performance exhaust shop and they did all the mandrel bends , supplied the collectors etc . for the bright work in stainless go to stainless steel fabricators or boat builders , given the quantities you require they will possibly give it to you .
if you cant get the 42 mm od get the nearest size bigger & have it crimped down to the size you require . good luck
many thanks for the link
the flange is a bit of ally sheet about 3mm thick has just been sanded 400 grit not polshhed yet the carb is monky metal anyiders what would bring this up..ps that is shiney spoty dog...nig, what grade of stainless are you using for this? 316L or similar?