I had the same deal when I bought my 94 325i...only one key (what do these people do with the others?). Got a new one made (actually they order it from like New Jersey) from the dealer...around $28 for the non-lighted key. I also snooped around my car and found out that it had the alarm system installed, so I went on e-bay and bought a 3-button key fob that was for my year and...now I can remotely lock and unlock the car.
You can find some locksmiths that can make a new key for you (it needs to be laser cut). They often use softer metal (like brass) for the keys whereas the dealer used steel or something harder (I don't remember the exact metal). Given this is a specialty key, you won't be able to go to the hardware store, probably best and easiest to go to the dealer.
<span style='color:green'>1994 325i </span>- - - 75,000 mi.
No mods - - - very happy as is!
<span style='color:green'>1995 525i </span>- - - 154,000 mi.
No squeaks or rattles... unreal!