You basically want an M12 wheel bolt with a 1.5mm pitch and a radiused seat.
The only wheelbolt I can find on the online etka tyoe site is:
Part No: 3A0601139
wheel bolt / M12X1,5X23,5
You might want to check that site out by the way:
http://www.vagcat.com/The info on there is priceless, I'm sure the parts guy at my local VAG garage hates me since I discovered that site. I'm always ringing him with a list of part numbers for obscure little bits which he then has to order in for me! In fact I'm going in tomorrow to pickup a complete set of new wishbone/arb mounting bolts.