OK, so I have a pre-facelift 1998 z3 1.9 auto.
It takes the old style keys with the transponder and key led light - see pic.
Today I went into my local BMW dealership with reg details, dvr lic + separate proof of address... wanted a spare.. just in case.
They charged me £62 for a new key that was ready and with them the very next day!!! ***Will not post so you must collect.
They work from your VIN, so if the locks have been changed and BMW didnt do it then they won't be able to help you.
Happy with the service!