better late than never:
http://www.megasquirt.info/PWC/lsupur.htm
VolksWagen dealers in North America sell a Bosch LSU4 wide band sensor for a ~$30. However this sensor is only inexpensive when purchased from North American sources. The Bosch part number is 0 258 007 057 or 0 258 007 058 (these are the same sensor, but they have leads of different length), and it can be purchased as a VW part number 021-906-262-B.