Can't help you with a shroud, but some advice on fixing one. We use these on teh rally cars and find that the shrouds crack quite often when new. Rather than welding them up, we 'stitch' then using small cable ties. drill 3.5mm holes either side of the crack, spaced about 1cm apart for the length of the crack and stitch it up using a small cable tie on each pair of holes. This allows the shroud to still have some 'give' and they eventually reach a point where they have enough 'give' to stop cracking.
ABS is one of the better plastics to weld, I actually do plastic welding at work and have found that later model falcon bumper bars are the worst to weld, I havent checked to see what the thermo shroud is amde out of yet.