I have an S2 flexi section here in EDI that you could use if you were desperate.
*BUT* (a) is it actually blowing gas - if not, it's not an MOT fail and you need to go stick it to them.
*BUT* (b) I wouldn't recommend fitting a replacement standard part because it'll just corrode away again - instead fit
http://www.ptp-ltd.co.uk/shop/ProductDe ... ductID=628 or any other s/s part (eliseparts no doubt sell one). Fitting the downpipe is not exactly a doddle (though much easier on S2 than S1).
If you just want to pass the MOT I suggest removing the damper, jet washing it until totally clean and dry, then refit it and get the car tested elsewhere.
TBH, I am surprised it's leaking - how many miles have you done in the car?
There are also some good deals on stainless 4:1 manifolds that replace the manifold and flexi section and with longer primaries. These make a nice noise and might even deliver a couple more Nm of torque here and there. The Piper S2 variants come with the correct mounting holes to refit the standard heatshield, which is neat.
Cheers,
Robin