karlos i make stainless exhausts for a living if only you were closer id happily sort you out i have all lengths and bores on the shelf i get them through longlife exhausts even the longest 4 inch bore ones are 12quid to us, unfortunatley my boss wouldnt let me mail one but he would let me fit it, might be worth contacting your local longlife centre tho they are all over the country.
oh and if your not bothered about looks you can mig onto stainless no problem with standard mild steel wire