I wouldn't change the axle, go for wheel spacers. You put them on the wheel hub then attach your wheel to the spacer/ They're usually done in incriments of 5mm and go up to 25mm, anything wider than that and you will have to get them specially made. Expect to pay about €100 for 4 20mm spacers. Im not certain of the width tolerance in an e36 but id say its about 240mm. So in an example, you could have a 220mm wide wheel and fit a 20mm spacer. Im not sure of the max distance so just check before committing to buy.
The ONLY Hellrot Red 323 in the world, emmm except for the other few thousand dotted around the world.