Hmm, not sure on the plastics.
I'm pretty sure any aftermarket front fairing or windscreen with a 6.5" opening for the headlight will fit. Buell Blast screens bolt right on, I've heard.
If you find a -real- Bandit 400 front fairing, grab it up quick. They are uber-rare. I've heard of some people grafting Ninja 500 bodywork on, but then, I'm sure you can fit just about anything to it if you know how to work fiberglass.
There isn't a huge aftermarket for the Bandit 400 anymore, not sure if there ever was. Occasionally you can find bits on Ebay, though.
You might try checking out Wild Hair Accessories. I don't have their link handy at work, but they used to have some fairings and rearsets that'd fit.