I bought a 370z... but it didn't come with the right key.

Redglare

Not to rain on your bad situation, but, you should have negotiated a spare key at time of purchase, when I bought my Z it came they were only offering me one key, after I negotiated the final price, I said take another $300 off or find me the spare key, guess what the 2nd key turned up while the car was getting detailed.

The moral of the story is; they will either find you a 2nd key or knock another $300 off no matter what the price you negotiated, they are always making money. ALWAYS.