Check out
www.movit.de , they have porsche brakes , i think johann has them on his /// M5 , they have aplications for E31
322x32 4S3
330x34 4M5
380x32 4M5 (damn , 380 , i think 19" rims would be necessary

)
The pic above is the 322x32 with 4S3 or 4M4 MONOBLOCK calipers with 75.5 cm² pads
This one is the huge 380x32 brakes with 4M5 calipers and 76,5 cm² pads , notice the titanium bolts and aircraft aluminium brackets... this one is a long distance brake set for heavy high performance cars ... guess 8-series fit in here ... I have nothing to do with the company , i just have had their brakes in my bmw and was very satisfied with them...
anyway here are some others ....
www.hamann-motorsport.de HAMANN Sport brake system for front axle
2 HAMANN brake disks 380 x 32 mm, vented and perforated, with vented DIN F52 aluminium made brake disk chamber
2 HAMANN four-pot fixed calipers in red (other colors available for extra charge)
HAMANN special brake pads
HAMANN Stahlflex brake linings
HAMANN adapters
Car must be at least equipped with HAMANN 19-inch wheels. The HAMANN Sport brake system can be additionally combined with the HAMANN Sport brake system for the rear axle.
also koenig-specials -
www.koenig-specials.com
seem to have a racing brake set , anyway no info about it...
In my opinion movit is the safest and best company for brakes...
Hope i could help