I think he is referring to those extensions you can get that go at the bottom of the bumper to make it a bit lower.
You could try
AC Schnitzer, they have this one:
I know JSN motors in joburg is the official distributor for ASC part here in SA, you might just try contacting them I am sure that should ship around the country.
You could also try
alpina
You can see the one they have in their
catalogue
Not sure if they have a supplier in SA so you might have to import it yourself.
You might also try some of the other BMW tuning guys like Hamann, Hartge or Vorsteiner (RGM is the distributor for vorsteiner here in SA but I am not sure if they have stuff for the older cars).
Most of these things will be pretty damn expensive, it might just be better to go for an M-tech II (gizmo on the forum has some for sale) or M-tech I (have seen a couple of them doing their rounds on the gum and junkmail) bumpers. Granted for these you will still need to change a lot op plumbing, but I think it will still be cheaper that the tuning houses options.
This is the M-tech II bumper: (Found this pic of my car with google

)
This M-tech I: