air (american international racing) sells rear flares but i'd be interested to find out where you sourced front flares - difficult to find, even with the boxster sharing the front fenders with the 996. wider is better.
would you say there's a big difference between flares made exactly for the car which seem smaller than a universal set of 4 and just forming it/cutting around the vents that would be around 3.5"-4"??
There are a couple pf companies that do 996 RSR kits(Getty Design, MA Shaw??). All of those front kits will work on the 986, and I'm sure that with the right $$$ they could work something for the rear.