First off, Welcome to the board!!
The best way to get a key for a 1997 318i would be to go to your dealer and order one.
I needed a replacement master key for my car when I got it b/c the original one was so worn that it wouldn't work properly in the ignition. I was originally trying to find one on ebay, and then someone pointed out to me that the key is not cut with a regular key-cutting machine (I think it's laser cut?). So I just went to the dealer. It was $28.00 for the master key and sub-keys were less than $20. Not too bad.
Good Luck,
Sean