Yes, most of the exterior panels are available new, except for the roof and some nose clip pieces. There are also patch panels for the front and rear fenders available (along the bottom regions of those pieces).
I think the differences between the CSI and CS are insignificant from a purchasing point of view. Given that it is primarily the intake side of the engine that is different, the more important criteria, in evaluating a car for purchase, is the condition of the rest of the car (which is the same between the two models with some USA/Euro differences), because that is where all the money will go in repair, new parts (not many interior parts available), body/paint restoration, etc. If you want fuel injection, then it may be better (potentially much cheaper) to find a very nice CS and do a conversion. There are also a lot more CS's than CSI's out there to pick from.
Good luck,
