You need p.n.
66-12-0-413-690 and 51-21-7-069-547
I've been told this is a dealer item only, but ECS Tuning offers it on their website:
Keyless Entry Remote Contact ECS before ordering
Brand: 
ES#:183805
Mfg#: 66120413690
Qty:
Ships in 1-3 days
$128.17
Slide-In Key Contact ECS before ordering
Brand:
ES#:89908
Mfg#: 51217069547
Qty:
Ships in 1-3 days
$28.29
I bought my car with one key only ... I was able to track down the the original owner after the purchase and he claimed that he dropped the car off with 2 keys. I believe that unscrupulous salesmen swipe the spare key and sell them on Ebay. Check it out ... there are tons of them! I wonder where they all come from ...