Widebody kits are not legal.
You have two choices of modding this.
One, go for a widebody M3 conversion. Get parts from Vorsteiner. Check with Boss Motorsports.
Vorsteiner GTRS3 Carbon Fiber Wide Arch Rear Quarter Panel
Two, do a "panel-beating" type of mod, extending the rear fenders out - Lim Tan has done at least 2 E92/3s on this mod.
Do note that your wheels' offsets will be entirely different after this mod. You need to change to a set of wheels which follows the new wheel-well.
For contacts, refer to the respective site sponsor folders.