All sorted now , it was me just being a bit of a numpty. I measured the diameter of the backbox pipe which was 2 1/2" and I wrongly assumed that the rest of the exhaust would be the same, but no! The rest of the exhaust is 3".
I've looked on eBay Nigel but could find anything!
So I'd do what gambit does and take it to your local exhaust fitter. Mine only charged me a tenner and that included new gasket, new bolts & a brew
Cheers guys