Took me ages to find one, then eventually one came up on ebay. Make sure you get the right one for your engine - the M54 and N52 are different.
If you get it from a breaker, check you get or be prepared to buy the grommet/washer that goes in the bulkhead (only about £7 anyway).
Good luck.... it might be worth seeing how much a new one from the stealer is...