They are not real bad to get parts for. The carbs are still partially supported with rebuild kits, but you have to source the odd o-ring and such. Luckily those KZ400 motors seem to last a long time so you still see them often enough, even though they weren't made in the numbers that a Honda 350 may have been.
Points are still available last time I checked. Most generic condensers will work.
Aftermarket regulators, rectifiers, and ignition coils are readily available, and probably cheaper than they were originally.
The biggest problem in the carbs is usually just a little rubber plug that goes over the jet opening. When that leaks they run real rich.
There are some tricks to getting the vacuum pistons to move freely, but there are several posts on that subject recently.
